I sold a closet by mistake and I need it back. Is it anyway to get it after the undo button has disappeared?

I don’t think so. You will have to start with the nuts and bolts, (from chests) and eventually make a new closet. Sorry, gamer! I accidentally merged two broom closets, and I really think I got more from the two lower level closets than I’m getting from the more evolved one. I usually try to keep the “producing level” items somewhat apart from each other, because accidents happen when they are right next to each other, and there is no way back after a merge.

Ask support, they may return it for you