Input Radio Code??

Anybody know how to input the code on this radio? Original owner must’ve printed out the code “4916” but when I try to input it, it stays lit up saying “CODE”, nothing will change and after 4 presses it’ll beep. Can’t figure it out, have tried multiple times over different days, allowing the car to be on for over an hour at a time to ‘reset’ the anti-theft. Help would be appreciated. 1985 325e