How to replace mast on power antenna? on 1995 Chevrolet Impala SS

Mast broke during car wash and I have replacement mast, but I cannot remove insert in housing.

Asked by for the 1995 Chevrolet Impala SS
the assm in under the rear kick panel, turn radio on and as ant is suppose to go up slowly pull mast out. the install while plastic inside hole with teeth facing the same way turn radio off and feed strip in until the gears start to accept , it will self adj after that
This is a front fender mount, assembly is under fender well
it repl the same unless you need to repl motor
Old plastic insert will not come out as new mast came with insert. New mast will not go into old insert. Thank you.