what do i have to do to make the trunk open ellectrically?

Is there a specific button on your fob that has the trunk symbol on it? I am guessing that there is. And if every other thing on your fob works try the fuse for the trunk open circuit

half way down on right, says 8, 21 click on image to enlarge

On older models of Mercedes you can reset many functions of vehicle by using the key to unlock doors from the passenger side. You turn amd hold the key in the unlock position until you hear all the locks unlock. Remove the key and try to open the trunk with the remote. You may have to repeat the passenger door lock two or three times. It's worth a try.

how to get the trunk to stay closed on a 2005 clk 500