Used to happen on my P2K. Used a rubber hammer. Gently hammer on the underside of the seat rails. You won’t do any damage and the seat post will eventually move.
I THINK he means to gently hammer the underside of the seat (with an upward motion), probably on the back side of it (more area to hit than the noes). Eventually it should come out. Might want to keep one hand firmly on the frame holding it down just make sure you get full effect.
I actually tapped on the back rails of the saddle with a rubber mallot in an upward motion. Had to do it any time I wanted to remove the post, and that was even after applying grease. Just use common sense and not over do it. You won’t break or bend anything.
My P2K post was always stuck. In contrast I’ve had the opposite problem with the aero post on the Kestrel Talon. It slips. I’ve found hair spray is a good fix.