This question is inspired by this question. In that question, one of the answer explains that you can predict if the soul is willing or not by means of some divination spells. It, however, doesn't address (so this question sparks):
How to persuade an unwilling soul to become willing to be resurrected again?
Answer that explain how to do this as PC is surely better than those that will only works as DM narrative/fiat.
I'm unfamiliar with after-life lore in Forgotten Lore setting, so if you think that will help explaining the answer, please do. If I'm not mistaken, I've read that a lawful good soul usually won't be willing to return because it's reached Valhalla or something.
Best Answer
Method 1: Have someone else raise them
Dungeon Master's Guide p.24, Bringing Back the Dead, suggests this exact course of action:
Method 2: Ask them in person
In most campaign worlds, planes are somewhere you can travel to. If you can find the soul and communicate with them, you may be able to change their mind. Finding them may be a challenge, and whether or not you can communicate with disembodied souls on their plane is up to the DM.
In some cases, souls don't pass on correctly, remaining as a kind of undead, and are much easier to find. This is especially convenient if you want to raise an enemy who returns as a ghost or revenant who will haunt or hunt you, so you don't even need to do much work to find them.
Method 3: Summon them
According to Monster Manual p.67:
It's not clear as to how long this transformation takes. It does describe lemures as twisted and tormented souls, which suggests that it may take some time, and devils are described as patient immortals who don't mind waiting for years.
Still, it is possible that your target will have transformed into a lemure by the time you have com, at which point you may be able to summon them with any spell which would summon a lemure, or, if it has been promoted, a higher-ranking devil. You may then be able to have a chat and try to convince them.
Method 4: Wish
Wish can do anything, although naturally this is a last resort.
Method 5: Divine intervention
Again, this is a last resort that can do anything, but your unwilling soul might come around to your way of thinking if their deity puts in a good word for you.