You enter the code on the station select keypad (the one you can remove
for security)

If you code was, say,  9851

 When CODE is shown on the display
Press button 1 nine times
Press button 2 eight times
Press button 3 five times
Press button 4 once

The correct code should be shown on the display

Now press button 5  to enter the code.

If you enter an incorrect code up to 10 attempts may be made before the
radio locks you out. You will have to wait 30 seconds between each try.