Very simple, there is a philips screw up through the center. Just unscrew and replace.
The new ones are MB # 126 810 00 12 9051 for black. The last 4 numbers are the color code and are needed to buy the part.
5076 = Blue, 8316 = Brazil, 8326 = Date, 8412 = Cream, 3112 = Red, and 7101 = grey.
Bosch Master, ASE Master, L1
33 years MB technician