HELP! GEarknob won’t go back on
 

Deleted as sorted it!

Presume you removed the knob by pulling the button out? You have to do the same when you put it back on so the tang on the button engages with the lockout lever. Try pulling the button out, hold it out while you lift the knob off and then push it back down, then release the button and it should engage again.

Did precisely that! Though it was more luck than judgement!!