I have an old router that very often encounters the problem of the bits getting stuck in the collet. Per the manufacturer’s directions I would loosen the collet nut and then strike the side of the collet nut with a piece of wood. I kept an old broken hammer handle just for this purpose and it has worked well. Note also to never insert a bit all the way into the collet and never strike directly on the router bit.
Lino Lakes, MN