To fix the leak and possibly replace the handle if you’re interested check this video. It may not feature your exact model but it will give you an idea of what you’re in for. I did this myself on both of our bathrooms at our old house with no issues.

youtu.be/MkPcCmYkG4Q?si=_VryQ6uZmwpj3lom

As far as reconfiguring the type of mixing etc… others have explained it pretty well. to me it would be a definite “call a plumber moment.”