is there any way to manually lower the seat as its not working?

this is a common problem on the mondy, The gear on the drive is made of plastic so the teeth just strip off, worst thing is that the part is not available on its own without the motor as well. you could remove the seat and try to strip it down to manually adjust the seat, but if you are going to do that you might as well fit a secondhand motor unit at the same time, fleebay might be your best option.