Who knows how to reset the radio on a 1999 BMW Z3?

If you mean to insert the RADIO CODE:

- the battery (on the car) must be charged or new;

- insert the key in the ignition and turn it on the first level;

- push the button ON/OFF of the radio;

- you will have 4 lines on the display;

- learn the code from the label you got together with the car's documents;

- push the buttons located under each line of the display, so many time until you get the requested number;

- after you have the 4 numbers on the display push the arrow "right" and the radio will start normally.