cassette original AM FM radio was unhooked. Now says C/D and i cant remove it. on 1990 Acura Integra

honda acura says they dont have a code sounds like radio is broken. I had the motor rebuilt and they unhooked everything to do it. Car dont have a C/D just cassette and i cant get it off to go to the radio. My question is whats up?

Asked by for the 1990 Acura Integra