If wrong codes already entered , then leave switched ON undisturbed until it resets.
Then enter code as follows
Switch Radio On -
Display Shows " - - - " Flashing
Press preset " 1 " repeatedly for 1st Digit
Press preset " 2 " repeatedly for 2nd Digit
Press preset " 3 " repeatedly for 3rd Digit
If the correct code number is now shown
Press preset " 4 " to Enter