Welcome to JUST ANSWER small engines, let me try to help you !!
You pulled the freewheel lever and the unit will not roll? The brakes are locked!! It has a mechanical disc brake on the transaxle, follow the brake linkage to the rear axle, just ahead of the wheel. See if you can get brake to release, you might have to loosen the two bolts on the brake caliper to get unit to release.
Get brakes released, then we can go from there , if need be.