I'll take this question to be about getting used to it after programming a suitable layout. I daily drive a keyboard with 42 keys.

How to get used to it? Patience and acceptance. You need to be patient. It won't be a quick process. And you need to accept that you will be slower for a long time. And accept that the coming period will be frustrating. You need to tell yourself this explicitly: I will learn this layout and it will be painful but I accept that this is the case.

A practical tip: do not go back to a comfy keyboard when frustrated. If you go back to your normal keyboard again and again, your muscle memory will not update as well (in my experience). Every time you go back you kinda undo some of the muscle memory updates (not science just my experience). Once you body gets that this is how it is now, it will adapt to this new normal and you will learn the layout.

Once I learned a non qwerty keyboard layout. That was one of the most frustrating things I have ever done (much harder than getting used to layers on a 40%). I got through it by accepting the frustration: you feel it, note to yourself in your head that this is indeed what you are feeling, breathe, accept it and continue using the layout. Slowly if needed! As long as you keep using it. You can only get good with it if you stick with it. I'm not saying that you need to go this route. But if you want to, you gotta get a bit zen with it.