Did the garage also repair the wear sensors, considering that the brake pads may have been replaced previously? Once the car or sensors indicate a need for replacement, or if the sensors have beyond their lifespan, they must be replaced to eliminate the warning, I believe.
The procedure to reset the brake service light for a BMW 520d (F10/F11 or G30 chassis) can be executed via the BC button on the turn signal stalk or the odometer reset button on the instrument cluster.
Essential Prerequisites:
Installation of new brake pads and a new brake wear sensor is required for the reset to function properly. The sensor is a disposable device that interrupts the circuit when utilised.
The electronic parking brake must be disengaged.
Your foot must be removed from the brake pedal.
Reset Protocol (utilising the BC stalk button)
Activate the ignition without initiating the engine by pressing the Start/Stop button once for F-chassis or three times for G-chassis, without applying pressure on the brake pedal.
Shut all doors and await the clearance of any preliminary warning messages from the instrument cluster.
Utilise the BC button located at the end of the turn signal stalk to go around the instrument cluster display until the date/time or trip odometer is visible.
Depress and maintain pressure on the BC button until the service warning indicators manifest.
Press the BC button briefly and frequently to navigate among the many service options (front brakes, rear brakes, brake fluid, etc.) until the preferred item is highlighted.
After the desired service is shown, press and hold the BC button one more until "Reset?" is displayed.
Depress the button, then press and hold it again until the progress meter completes and "Reset Successful" or "Resetting" appears.
Deactivate the ignition. The warning light should now be extinguished.