Check if it's the track "frozen" or if the track won't move because the sprocket won't let it. The fix depends on what's wrong. If it's the track is frozen with rust, you can soak them in water to loosen up the frost - not anything oil-based; just plain water.
If the sprocket and internals won't turn (maybe just a degree or two of backlash), then you'll need to dismantle to determine the root cause. I'm not familiar with this model but if there is a cover you can remove to get to the brake drum on that side, you can check if the brake band is stuck to the drum, even though you soaked it. You can also attempt to roll the drum/shafts back and forth to see what's moving and what isn't.