You to gently insert a screwdriver in to the side of the plastic
covering  push the tab out. You could also get a long nosed pliers and
squinch the tab from the back - and push it out.

the changer would be very expensive to have repaired.
its not a simple belt or other cheap item.
delco parts are only sold to delco dealers and they know it, they also play
extremely dumb when its a simple fix.
you will be charged 1/2 of what a new one retails for in the parts
department.
That is how they figure repair costs
They also probably wont fix it right or mess up something else.

its best to repace it with a real stereo from the aftermarket.

have the local stero shop you will buy the stero from install it