I have completed my book. But I'm stuck writing the prologue. I've written the story with narration by the writer (not from the point of view of any of the characters).
But I don't feel like that works for the prologue. I thought I could have one of the characters narrate the prologue, as though telling the story to somebody else, but I don't want to go and change the entire book to that character's point-of-view.
How should I write the prologue so that it works with my main story?
You are allowed to have the prologue narrated by a different character as long as it is absolutely clear who the narrator is. You do not have to change the whole book. In fact, every chapter can be a different viewpoint narrator; George R.R. Martin does this throughout his Song of Ice and Fire books.
You can also have the prologue written in third person omniscent even if the rest of the book isn't. Prologues and epilogues, being set off from the main text, have a little more leeway.
Yes, of course you can, and you don't even have to make it clear who the narrator is.
You're the author: decisions like this are yours to make.
Prologues are prologues because they break from some element of the book proper--different time, different place, different narrator POV, different something.
It sounds like your best choice might to be write your prologue from a more distant third person POV, maybe even an omniscient POV.
(This is assuming that you need a prologue.)
