Pee stains can be removed with any enzymatic spot remover or car upholstery shampoo. I use Vanish spray or Zip car (upholstery) shampoo. Enzymes will break down the smell.

Another alternative is vinegar and water, 50/50 mix.

You need to block him from accessing the sofa until he is littertrained and neutered. Buns like peemarking sofas and beds. This tendency might not go away with neutering, but it could.

You should also start littertraining him immediately. It’s difficult to get an intact young bunny perfectly litterbox trained, but the sooner you start, the better. If he has a big area to move around in it can be best to make it smaller by using an x-pen. Put poop and sth he has peed on in the box. Preferably place it where he has gone before – or if he goes outside the box, move the box to that very spot. Placement of the box is very important for rabbits. They choose a toilet-spot, and they will go in that spot regardless if there’s a box or not. Most buns catch on pretty quickly.

Thanks for reporting back, Aimeenb45! It’s really good to hear these positive updates. It does help validate the usual advice given. It will hopefully encourage others that are currently facing the issue you were.