You could try tapping in wooden/plastic shims while prying upwards using the holes in the platter. Try hitting the spindle with a wood block and mallet to loosen.
Alternatively, gently pack cardboard under platter and leave it on while moving.
Help! Monolith turntable platter removal
I'm preparing to move house and wanted to pack up my Monolith turntable so I began what I thought was a simple process of disassembling the turntable. OK - it's not that simple. Can anyone guide me in removing the platter? I made the mistake of first disconnecting the drive belt, and now it's loose under the platter.
I emailed Monoprice, but don't know if their customer service is any good, so I thought I might get advice here.