Tap on the nut to drive it upwards, then, insert a thin screwdriver into the slot to pry collar loose. Not too much pressure or it may crack.
Borrow or buy a gear/bearing puller from a mechanic or car accessories shopMy 1/2 inch router bit is fully stuck in the collet alongside the nut. I’ve tried torching it tapping it on its side, WD40, putting it back in the router but it doesn’t budge. Does anyone else have any suggestions?