Had to force it.

Can he just take it out and reinsert it correctly? Thank you!

He'll try that tonight. I ran another load through the dryer this afternoon, now it's stopping after 10 minutes of drying. The timer says 1 hour, because I can't change the selection from Towels/Bedding, but it shut itself off after 10 minutes. The back of the dryer gets hot at the top, stays cool in the middle and bottom. Surely that isn't connected to the knob being on incorrectly?

No, it started immediately after shutting off & ran for exactly 10 minutes again.

We're getting to that point, too. We figured out that the dryer was shutting off because I kept starting it with dry clothes in it, instead of a wet load of laundry. My fault :o. But he re-installed the knob and it worked like normal right when he did that, but when we tried to run a load of towels through about an hour later, the knob wasn't working again! I guess he could have damaged it the first time he installed it incorrectly - can we buy the part to fix that, or would we need another new control part? He wants to try to fix that, but if we're still having problems then we'll call someone out.

Thanks for all your help!