There's probably a safety switch. [https://www.youtube.com/watch?v=-s0L-n23WdQ|This] video features a different model but the guy shows you how he found the switch to unplug.
[https://www.garagejournal.com/forum/showthread.php?t=200559|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!