If you can get to the control module located on the offside rear post (if you have a side conversion it can be difficult) then the 4 pin plug has both +12 volts and earth as well as the motor wires on it so you can jumper them across to manually control the motors, and assuming you have +12 volts source from a battery then
The plug is M2-01 on the diagram below, look at the lower section and each plug is indivdually shown;
1A is Earth & 1C is +12 volts
1D & 1B Blue and Red are the motor wires
If you connect 1A to 1D and 1C to 1B
OR
if you connect 1A to 1B and 1C to 1D
Then the motors will operate up and down for you