Locomotion via Swimmingmoves

Hi there,
i´m currently working on a underwaterscene trying to implement locomotion via actual swimming moves. I´m new to real time dev and have absolutely no idea where to start. I have already set up the VR Expansion plugin, that kind of has some armswing mode, but i´m to unexperienced to modify it properly.
Every hint would be very welcome.
Thanks in advance!