Start a mini dirt bike with no pull start?

So I picked up a cheap little dirt bike bike for my son as his first bike. Was told just needed a pull start. So I ordered an alloy one and anew flywheel. Once I got the cover off I realised the last owner has stripped the flywheel bolt so I can't get that off. So I'm pretty stuck

Is there anyway to start these little things? The bolts only a 10mm too.

Start a mini dirt bike with no pull start?