Is the cylinder head aluminum or cast iron? (Pray that it's cast iron.)

Core plugs, a/k/a freeze out plugs, are pressed into their cavity.

I suggest you be very cautious and circumspect about this job for it
will be difficult in any instance and the only reward is to cure a very
small coolant leak that's NOT going to "blow out" catastrophically
anytime soon. I would first understand exactly what's involved in
installing the replacement plug before even touching the leaking one. It
may be better to add some "stop leak" to the cooling system and just
drive it.

    I've never done in a Mercedes but the way I would do is to tap on the
lip (without harming the block) until you manage to bend it inwards a
bit, relieving some pressure.  Then, tap on the bottom of the plug
closer to where you bent the lip so the plug rotates: the side you are
tapping should go in a bit. The side that is being raised, you can then
grab it (vice grips/whatever) and yank it out.  Clean the hole on the
block, inspect the inside, then put a new plug in place.  BTW, I only
use brass plugs instead of factory ones.  I am that crazy.  In any case,
you need to find a socket/pipe that would fit inside the new plug almost
snug (if it is truly snug it can become very exciting quickly). You will
tap the socket to press the new plug into place.

It is not hard but you need room around the plug