The fan is retained by an olive (or compression) fitting. The more you try and pull the fan forwards, the tighter it gets. Most professional repairers have a small “puller” that will do the job; however in your own case you will have to douse the fan centre with WD40 and after waiting a while see if you can drive the fan BACK, away from the olive. If it goes, the olive can be easily removed and it will all come apart.
Needless to say, power off………..
Regards,
Pengun45.