The book describes Strahd having two methods of gaining information.
Strahd is able to scry on the characters. This is his best method for knowing about the party's adventures as you play.
Strahd has many spies who report to him each dawn and dusk. Among these are many of the Vistani. The Vistani are the only people who can enter and leave Barovia at will. They are probably Strahd's best source of information about things that occur outside of Barovia.
Given this mundane method of gaining the information you want him to have, there is little reason to metagame the crap out of this.
Talk to your players
Just...step out of character for a moment and talk to them. There's no rule that says the DM can't help players remember the features their characters have. If you're more comfortable doing it outside of the game, then chat with them in private (in person, text, chat, whatever).
If you were trying to teach someone how to play checkers and they clearly forgot that multi-jumps are possible...if you want them to learn how to play, you remind them. There's no rule that says that once the game has begun, everyone must muddle through on their own.
Learning D&D is a process...and knowing how much to help with that process depends on your players. As a DM who has run for a lot of new players, I routinely have to remind my players of all the things their characters can do. Because these are things the character should know but the player does not.
Your concern that this strips away player agency is not something you need to worry about. You are not mandating that they do something, you are not taking away their choices. You are simply pointing out that another option exists.
So, here is what I recommend.
Ask them if they'd like input from you.
Go with something like...
Hey guys, I know you're all new to D&D, so I wanted to ask you something. I've noticed there are times when you guys forget about some of the stuff your characters can do, or you get stuck on something that has an alternate solution. I know D&D can be a lot to handle all at once, would you like me to help remind you?
If they say yes, a simple "Hey, just in case you forgot, your character can cast Mage Hand...which is kind of like short-range telekinesis." or "Hey, just a bit of advice...when you see a bunch of enemies in a clump like that, hitting them with an area of effect spell, like fireball, is usually a good idea."
For more complicated things (such as breaking and entering), I will call for a check that provides a hint right in the call. To give a recent example, the party was looking at this well-secured building, trying to figure out how to get in. So, I said to the party Rogue...
Give me an Investigation check to case the building, see what your options are for breaking in.
The rogue knows how to break into a building. There's no need for a check to see if they remember how to make locked doors stop being in their way. Instead, I called for a more specific check to determine how good of a job the Rogue did at picking out the specific vulnerabilities of this building.
Even if their check wasn't great...that still plants the idea in the party's head of "what other ways can we break in?"
Checks should be for things that challenge the character, NOT the player
What I would NOT suggest is calling for rolls for your characters to remember what they can do. Just tell them. This is not something their character has to try to remember or struggle to recall. In the example of Mage Hand...that character has cast that spell a vast number of times during their training...remembering that they can cast that spell is not 'challenging' for that character, it's hard for the player. Dice rolls should be about the character, not the Player behind them.
In Summary...
D&D isn't a competitive game...the DM is yet another person who is working with the party in order to make an engaging, fun game. The fact that they run 'the enemy' doesn't matter. You aren't their foe, you aren't trying to beat them. If their lack of experience is getting in the way of them having a good time, then volunteer to help!
Best Answer
No magic can prevent it from working
The revenant's statblock (MM, p. 259) describes the Vengeful Tracker trait as follows:
It's not described as explicitly magical. Even if it was, though, the Monster Manual mentions outside the revenant's statblock:
The fact that "No magic can hide a creature pursued by a revenant" means that there is no spell that can prevent the revenant from knowing the distance to and direction of its target.
...and neither does "killing" it (unless you wish it to pass on within the next 24 hours)
In addition, as the last line states, even if you destroy its original body, it'll simply seek out a new one and keep coming, as explained in the Rejuvenation trait in its statblock:
As stated, the wish spell can explicitly be used to force the soul to pass on between its body being destroyed and it being able to inhabit another one. (Of course, wish can do anything at the DM's discretion, but this line makes it explicitly within the purview of the spell.)
Your best bet is to outrun it or trap it without killing it - for a whole year
As another part of the description outside the statblock states:
The revenant has a strict time limit within which it can accomplish its goal: 1 year. If it doesn't get its revenge by then, its body crumbles and its soul passes on.
Thus, your best bet at avoiding the revenant's vengeance is to either trap its body (in a way that it can not kill itself, if the DM deems it intelligent enough to do so) for a year, or simply continue to outrun it for a year. You might be able to do the former with a spell like imprisonment, though it's a 9th-level spell with a material component that would need to be worth 8000 gp (it must be worth 500 gp per Hit Die of the spell's target, and revenants have 16 Hit Dice).
This question discusses what magic items can be used to trap/ensnare/capture enemies. In addition, this particular question about how to permanently kill/stop revenants has been discussed in a few places around the internet:
I haven't gone through their suggested solutions in detail; in short, they generally suggest specific ways to outrun or trap the revenant.