I’ve had to use 2 pipe wrenches and heat in the past. Pour hot water into the hook slot, let it sit, WD40 may also help if you’ve gotten electrolysis between the aluminum hook and steel shaft. Tap the hook up to get it out of it’s seat with a hammer then use the pipe wrenches. Look at another attachment to be sure your going in the correct direction. If this doesn’t work you could use a torch to heat up and expand the aluminum dough hook. Just don’t melt the mixer’s lower oil seal.