How to reset the air bag indicator on a BMW 3 series E90 more precisely BMW 318i N46 but this procedure you can use for almost all models.
This indicaot can only be reset with a diagnostic tool. I use maxidiag elite.
I turn on this tull and conect to car jack.
Now go to BMW.
Then go to 3 series.
Next menu at number 4 you have E90 / E91 / E92 / E93.
Now the diagnosis tool will establishing vehicle communications.
After that you must select the model for your car in my case it was a BMW 318i with engine type N46.
Now you must select the version, i select the EUR_RHD this means European Right Hend Drive.
On main groups select control units, on part menu select number 3 body, now you look for SRS or MRS in my case wat multiple restraint system.
Now you got in function menu, you canr read codes to find out the MRS airbag warning light is on or you can erase codes.
This is the full procedure how to reset air bag on BMW 318i E90.