Chosen Solution

12A1869F011 Self propelled mover will not go in reverse. Please help.

There’s probably a safety switch. This video features a different model but the guy shows you how he found the switch to unplug. This is a more in-depth discussion, some of which discusses how much of a good idea it might be to disable the safety feature completely. However, they’re talking riding mowers, and I imagine it’s a different scenario with the model pictured here. Still worth a read. Good luck!