Assuming it is the same as the 928 seat base, which I think it is, there should be a manual drive in the front center(ish) area just below the front of the lower seat cushion. this is a partial bevel gear that you drive with an Allen wrench. do not try to drive it fast with a drill or similar. it will be slow going when driven by hand, but trying to drive it fast runs the risk of damaging the gear since it is only a partial gear and therefore has intermittent engagement.
