There are programs that can get the password for a router, but I don't even know where to start, or even a name to give you, not to mention you'd probably have to learn a lot about how to use it. My cousin used one once but he's some kind of computer genius, and anything he tried to explain about it was all Greek to me. Hell, I don't even know if that's legal or not. It would probably be wise to just leave this option alone.
You'd have a much easier time explaining to your dad that port forwarding doesn't do anything to your computer (if that's the case) or just asking him to do it himself so you don't "screw anything up" like my dad used to think I would do (and to be honest, when I was younger I probably would have).