It appears that they skin covering the white plastic ear liner is somewhat missing. I would trim the plastic so that the available skin will cover the edge of the ear when super glue is used to adhere the back skin and the front skin of the ear.
To replace the antlers, first open the back of the head, it should be sewn in a "Y" pattern with the tips of the Y starting at the rearward base of each antler and joining together at the back of the head. Remove the antlers and refit the antlers with the new ones. RE sew the Y incision after screwing the new antlers in place and after a little grooming it should be completed.........Buzzi