It's in the manual.
You just reset it and then drive off. The light will go out in like a mile and now it has recorded the new tire pressure.
If this isn't working, it's possible the shop damaged the TPMS transmitters. I guess a really low pressure might make it error out potentially...or an excessively high one, although I've never tried.
What is the tire pressure?
Also, why didn't the shop reset it and verify that it was working? Any good shop should do this.
Also - from what I understand, BMW had a superior system that would actually tell you the tire pressure per tire as opposed to just green or red. It did not meet the "idiot use level" required in the US. So I guess you can blame us for the overly simplistic design.