Switch radio on, press and hold SELECT and wait.

Or:

BM53 with Widescreen board monitor:
• Turn on the radio.
• Within 8 seconds, press the “INFO” button.
• From the info screen select RDS
• Press and hold the BM control knob for at least 8 seconds.
• Scroll through functions using the station < > search buttons.
• Turn off the radio to end the service mode