Ocean Monument Finder
Edition
Version
Seed
Three elder guardians, wet sponge rooms, and eight gold blocks hidden in the core, all under water.
A monument needs deep ocean under it and ocean or river for a wide radius all round, so it will not squeeze into a bay or a small sea.
On Java Edition, type /seed in chat (it needs cheats on, or operator rights on a server). On Bedrock, open the world's settings: the seed is listed under Game.