The rules of antichess specified in Wikipedia state that the rules of regular chess should be followed except
Capturing is compulsory. When more than one capture is available, the player may choose. The king has no royal power and accordingly: it may be captured like any other piece; there is no check or checkmate; there is no castling; a pawn may promote also to king. Stalemate is a win for the stalemated player.
It doesn't specifically call out who would choose what piece a pawn gets promoted to. It makes sense to me that since the game is antichess, when you promote a pawn it is a bad thing and your opponent would get to choose what piece it should be. Is this the correct way of playing or do you get to promote your own pawns?