I’ve had to do this a few times. Wrap cake very generously with glad (seran) wrap; 3 or 4 times folding in the corners and keeping it nice and firm. Make sure u go underneath the cake as well. Then cover with a few layers of alfoil (tin foil) and use masking tape to secure. Freeze. To defrost, I put a towel underneath a drying rack and pop frozen cake on top in room temp. Do first thing in the morning and you should be able to decorate in the late afternoon/evening. All the condensation will form on the alfoil, so just wipe it away before removing. If your cake is still cold to touch in the centre after you’ve unwrapped it, then it’s needed longer and you’ll need to leave untouched under a fan til it is defrosted and dry. Good luck