It should reset whet pressing the roll bar switch to the up position as you have tried - it can take a good 10 secs of pressing to wind the mechanism back up & re-engage.
Try once more keeping the switch pressed for longer.
If it still wont reset then the next thing will be to have the car plugged into Mercedes STAR diagnosis to check & clear the fault codes.
Let me know if you need anything else.
Best regards, Paul