On the left side of the toilet (looking at it from the bowl) there should be a hole.  I don't remember if it requires an allen wrench or socket, but I found it very hard to operate.  Remove the cover in the back and make sure there are no lit lights indicating a problem and requiring a reset.  I do not remember the steps to take if one is lit, but it should be in the manual.  I, also, found that the micro-switches for opening and closing were the cause of my problems.  You had to remove the toilet. Never could get them adjusted correctly and neither could a good RV repair tech.  Replaced it finally with an old style foot pedal flush.
Roy Warren