Definitely get a patch kit and take care of the liner before things get worse. There are various kinds of liner kits that be applied even underwater. For the outside, that hole appears to be small. So unless I'm mistaken, it's more of a cosmetic issue and you can use just about any epoxy-type product to fill it in. If the hole was large to the point where the pressure of the water could try to push out through the hole, then you would need to try to get behind the liner and perhaps slip a piece of metal in there to provide support. But from the pic it doesn't seem that large to me.