The question asked here is a bit different, in that I think the OP is asking to swap in their PGY-2 0 -- i,e. complete their PGY-1 where they matched, and then swap for a PGY-2.
In that case, you simply do your PGY-1, and then sometime (usually after Jan 1) start looking for a PGY-2 in another area. It's not simple to do so. If your PD helps you it's much easier. You don't need to swap per se -- your PD will be trying to fill your slot. It can get painful -- your PD could fill your spot while you don't have a new one, and you could get stuck with nothing.