How do I replace placeholder sprites

I’m making RPG game and I used placeholder sprites. I made my own sprites now they have the same layout. How can I change the sprite without remaking the animations for the player?

Simply save your new image files over the old ones. (i.e. in Windows, not in Unity). Unity will detect a modification and reimport the sprites but, if they follow the same layout as rbe old ones, your animations and references should all remain intact.