Hi Paul.....welcome to the Club
Sorry for the late response, good to have you onboard
Sounds like it has over-extended the drive rod. First check there is no obstruction underneath the seat (e.g. something dropped into the area such as a bottle or umbrella)
Possibly try operating it with someone gently pushing back with their feet against the front footwell and see if it can be persuaded back off the rest point.
Cheers, Trevor