https://www.skandix.de/en/documents/...ssion/3000478/
The button can be replaced without removing the gearknob . It is more difficult to be sure that the button lifting pin engages in a detent in the rod of the gearknob . Once you have the old button out it is obvious how the thing works.
The above link is a good pictorial on how to pry the button out and dismantle.
To remove the gearknob first unclip the gaiter. I think the later type is a quarter twist and pull down
Then grip firmly the gearknob and give a good hard tug upwards .
WORD OF WARNING ! Keep your head well out of the way . Many have had black-eyes , fat-lips or broken teeth .