Is it possible in some way to adjust the motors of my seat manually, particularly the up/down position?

Recently the height adjustment in my drivers seat has gone rogue, and I was curious if I could lower it manually somehow?

 

As the gearing works, motor to screw shaft, you will need to remove the motor to allow the screw shaft to turn. That would mean removing the seat.

The plastic gear on the motor is known to go bad. You probability hear the motor spin but nothing moves. Brass gears are sold on eBay. There a number of posts dealing with this repair.