Stuart - Sorta easy. I removed my seat (I had the same issue at the bottom, LH side) so I could work on a bench. Got a heatgun to warm/soften the vinyl - including about 4" on either side of the derailment .. Get a wide plastic spatula/putty knife, etc to push the vinyl back into position .. Now the tricky part: take a plastic or rubber mallet and pound the edging back onto the seat frame/vinyl cover combo while holding the vinyl in place. (..you may want to push the vinyl past its natural position because the edging is going to push it back out again..)
The factory has the advantage in that they appeared to glue the vinyl to the seat frame before pounding on the edging. Mine is 90% cosmetically good, but secure.
Jim