Not that I know anything about Thor models, but by backtracking the slideout bar, you will know where to cut into the belly covering. On my MS, I had to go in about 3-4' into the covering before I got to the rollers. I have no idea how yours is set up, but there will be an electric motor in there somewhere with long, square metal bars going to the other bar. Barker may be the brand on your gear motors...
If the motor is turning, then the gears are stipped, or the bar is broken. It may be no more than a shear pin gone, or the motor itself.
It isn't too hard to figure out once you get it uncovered.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired