I'll assume that your fuel distributor is similar to my M103 engine. First, you'll have to remove the fuel distributor from the engine. Should be a few torx or allen bolts on top of the distributor (and remove all of the fuel lines).
There's a 19mm nut in the center of the bottom of the fuel distributor. Remove that nut and you can pull the plunger out of the fuel distributor.
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino