I’ve had mine for over a year now and I never bathe him...or do anything with him ever, really. It’s a rarity that I actually see it out and about, he’s usually hiding in one of the various tunnels he’s dug out for himself. Just change his food and water dishes and he’ll do the rest
There's no good reason to bathe hermit crabs, it's really just an old practice that people have carried on because of memory, or by what inexperienced keepers tell them.
I do not take my hermit crabs out of the tank for any reason, not even to hold them, which makes bathing absolutely useless and unnecessary to them.
They actually store water in the back of their shells, which does have perfect mixtures of fresh and salt water. If you spook them, they can dump that water out on you.
When you place a hermit crab in the bath, like when you watch one on YouTube, they usually scramble around frantically, which makes people think they like it.
They are actually freaking out, trying to find a way to escape. I used to bathe some of my old crabs but stopped that practice entirely over a year ago.