This depends on how the loco's creator set things up and unless you're an advanced expert you won't be able to change it.
With most locos the wipers don't work. With some other locos they work automatically when it's raining. I can't remember seeing any locos with operative in-cab wiper controls but AFAIK it should be possible. I have seen a loco with an in-cab control which operated a little fan to keep the driver cool, which presumably is a similar type of thing.
John