Use a pair of small vise grips in your dominant hand to hold the center pin as close as possible to the base. Use your thumb and forefinger of the other hand to hold the rivet in place. Pull the pin out with the vise grips, doesn't take much force. Trim excess flush with a pair of diagonal cutters or a razor blade.

One of these days I am going to try a generic pop rivet tool on one of these BMW fasteners - suspect it will work fine.

Had to replace the front inner fender liner once after hitting deer with X3. Have to give BMW credit for employing inexpensive and simple fasteners.

Ub