I did this on my last car (F20), same wheel as the F30.
It was really hard first. Next time when I knew how to do it was easy.
Locate the spring with the screwdriver and push it in. Pull the airbag on the same side. Keep holding that side out while you do the same thing on the other side. This time when you have pushed in the spring and pulled out the airbag it should come out a bit more. Then switch side again, hopefully you should have got it out by now.
F31 320dA Sport Line - Gone
F20 116d Urban Line - Gone
R56 Cooper S LCI - Gone
E87 120i M-Sport LCI - Gone