If you are not able to move the slide using your 'manual' over ride option.
Remove all 12 volt power to the unit and have several people push/pull the slide out when you are ready to work on the motor. From what I have been told and read, the motor(s) have 'brakes' that are 'on' when there is 12v power to them. Remove all 12v current and the 'brakes' will release. this will allow the slide to move in and out by push/pulling it. Remove the 12v power by having the camper unplugged from short power and disconnect the 12v battery.
2013 Forest River Salem Hemisphere SBT312QBUD
2001 CrewCab F-250 7.3 PowerStroke Diesel
SuperChip, BTS transmission, 6.0 Trans Cooler