There is a trick to do this... This is a known issue when the platter hasn't been removed for a long time...
You need a big screwdriver for this, at least one with a big handle.
Stick both forefingers through both holes of the platter and apply a little uplifting force so the platter moves just a few millimeters up. Now keep applying upwards force with one finger while giving a tab with the BACK of the screwfriver vertical to the axle of the platter...POP
I'll add this soon to my tutorial about the Technics maintenance
. It need to be just on top of that page before the text about opening the black top cover.