There is currently¹ no way to do this in the rules.

If you're trying to avoid damage resistance, there is a feat that can help you: Elemental Adept. It lets you choose an elemental damage type, and spells that deal damage of that type ignore resistance. So, for example, you could take Elemental Adept (Fire), and your Scorching Rays would ignore fire resistance.

If you're trying to get around damage immunity, or exploit damage vulnerability, then you're out of luck. The only solution that currently exists is to pick spells with different damage types so that you always have the one you need.

Of course, this is D&D, so you could always ask your DM if they're willing to houserule something that would let you swap elements the way you want to. A metamagic option for the Sorcerer makes the most sense, but balancing it could be tricky. A Warlock invocation might also work here, but balancing it would be even harder.

¹ Current published materials: DMG, PHB, MM, Elemental Evil Player's Companion.

Embrace it

I play a human cleric in a party full of characters with darkvision. Granted, we don't find ourselves in pitch darkness all that often, but it happens enough.

Rather than find a way to level the playing field, I find that embracing this difference makes for some interesting narration and adventuring.

Roleplaying

I have to trust at least one other character enough to have them lead me through darker areas. The DM can get creative about how this works, without being adversarial. For example, they might say, "those with darkvision see some slippery ground up ahead." But if whoever is leading me forgets to explicitly relay this information to me, it's DEX saving throw time.

This is actually a plot point: there is one character in the group I've known for longer, and so I trust them more, and usually have them lead me. This is just one more little detail that adds to the reality of our world.

It's important to note that this is something we'd discussed ahead of time — don't just spring this on your players. Even though I, as a player, hear the DM say something, I am perfectly happy to go along with my character not knowing it. Your monk might find it silly, and not like the idea.

Establish, through a couple of examples, what might be reasonable in such a situation. Maybe they don't want to constantly be saying "I tell the monk about that thing you just said. I tell the monk about that thing too. I tell the monk about this other thing." You might all agree that unless there's a reason to be quiet (eg. stealth situations) it's said by default.

Sometimes it's an advantage! My cleric will often try to use other senses eg. explicitly telling the DM "I listen carefully for sounds of activity above," or "I inhale slowly through my nose, trying to smell anything other than the dankness of the cave." On more than one occasion it's led to sensing something no-one else did, because they were all looking for something. Again, this was a detail the DM thought about in advance. You should think about your settings, and identify things that the characters could sense, but would miss without specific attention.

Combat

Combat is tricky but not impossible with appropriate tactics. Encourage your players to think about this in advance. Many of my cleric spells have "a creature you can see" as a valid target, but not all, so I have to plan what I might do if I can't see anything. Maybe the monk has abilities that will work blind.

Being a cleric, I can use the light cantrip on my own mace or shield; maybe your party has someone who can do that too. If they do this, describe the combat to your players! Think about how bizarre this would be — a glowing mace or quarterstaff flashing around, flying from creature to creature! Shadows of goblins and kobolds dancing large and small on the walls! You've really got some opportunities for creativity here.

Mundane doesn't have to be boring

Torches are mundane, but you've still got to remember to buy them. And if it's been a long time since the last town, your monk may have to decide whether this is the time to use their last one.

Many solutions may have a price: will the whole party want to risk breaking cover just to accommodate the monk? Again? (Don't foster PvP sentiment just for cheap conflict, but this can still be interesting).

It's already a given that your party comprises characters of different classes with different abilities in combat, and during roleplaying. Sometimes this can cause issues and make a single player feel a bit useless, it's true. Completely levelling one of the senses to get around this might smooth over exploration and combat, making things more fun; OR it might close off a bunch of opportunities for the party to work together, strategise and build the reality of their world.