Here are some basic installation instructions for turntable belts.
1.) Remove rubber pad/mat.
2.) Remove platter just beneath mat.
2b) Some platters are "press fit" onto the center shaft and seemingly can't
be removed, the trick is to lift up on the platter while simultaneously
lightly tapping on the center shaft with the handle of a screw driver.
3.) Use a rubbing Alcohol soaked cloth to clean outside of large 'lip' or
rim underneath platter and the (usually) brass pulley shaft on
platter drive motor which should now be visible.
4.) Install belt around the rim underneath platter. Belt should be
somewhat snug without falling off.
5.) Optional: Clean then Lube main center platter shaft of turntable
with 3-in-1 oil or similar.
6.) Re-install platter.
7.) Look through 'access window' in platter and rotate platter until
motor pulley becomes visible.
8.) Stretch belt from platter rim over to far side of motor pulley.
9.) Re-install mat and start player.