the car is a 2000 328i, bought used and do not have the radio manual. got the code last week, just do not remember how to input and l need to replace the battery

Push down the button on the panel for the code.Then push enter.

hook a battery charger (or extra battery) to the cables for continuous power while disconnecting the battery and save all your settings.

not sure about yours, but on a old one like mine it can be a real hassle to reenter the code. seems l have to wait 24 hours because l entered it wrong.