I agree. I thought it was funny that until IMRight's post number #43 no one could figure this out. Just blowing ballast on the sub would raise it unless there was catastrophic damage.
Pump water from fwd trim tank to lift the bow, if still stuck below.
A little reverse thrust.
Pump (or blow, if you're not worried about noise) from trim tanks or the aux tanks) to get a little light is safer than blowing HP air into the ballast tanks. Else the ballast tanks might leak the HP air.
On the surface, ride the vents while pumping them from the LP blower and monitoring from the periscope. Once stable, then open the hatch and run on the surface.