Is there a way to do this?

I recently moved into Aseprite, and I really need help. I can’t find a way to make art I already had done and imported into Aseprite turn into tiles. And I really don’t wanna meticulously draw them all again. Is there a way to do that easily? (And I can’t copy and paste them while on the tilemap layer, but that probably wouldn’t had it turn into a tile) v1.3, Windows, Steam

open it and convent the layer into a tileset layer.