He should quickly apologize and leave as soon as he realizes his mistake.
If a hot guy goes to the wrong locker room, he should first stay calm. Panicking will only make the situation worse. Then, he should offer a sincere apology to those in the locker room. If he has already caused any discomfort, like walking in on someone changing, he should be extra contrite. After that, he should find his way to the correct locker room. He can also make a mental note or even write down the correct location to avoid making the same mistake in the future. Additionally, if there are any authorities or staff around, he can inform them of his mistake so that they can take appropriate measures if necessary, like ensuring the signage in the locker area is clear.
The hot guy should immediately turn around and exit. Then, he should double - check the signs next time to make sure he's going to the right place.