Assuming you have checked the sending unit or sensor for its working condition, go to your MB dealer and get the tool for pulling the panel. I tried the other ways (coat hangers, etc.) and the time you'll save, not to mention your dashboard or cluster, isn't worth the 8 to 15 bucks you'll spend on the tool. It is used for other jobs as well. Search on the tool's part number and you'll probably find the other functions.
When pulling --- Don't yank too hard! Slow steady pressure does the trick. Sometimes, one side then the other will help. Don't yank.
You may have to remove the carpet in order to see the cable as it goes down to the transmission. Keep an eye on that cable. Check it for freedom of movement.
That said, once you have the cluster out a bit, be sure to check the slack in the speedo cable. Mine moves fairly easily.
Unscrew the cable from the speedo before pulling out too much.
Be aware that when reinstalling the cluster, you may have to help pull the speedo cable from below the dash to help the cluster to slide in. Don't just push it in without checking the cable's movement. You might bind the cable and if you do, you'll get speedo needle bounce at low speeds.
Also, depending on the age of the car, I'd replace the bulbs while you are back there and clean the electrical connections with contact cleaner. Might as well since you are going to have to do that at sime time in the future. Small price to pay.
Finally, if the car is older than 5 years, take another ten minutes and replace all the fuses and clean the contacts. Don't just assume they are good. Replace them with new ones. Also, remember that fuses are not just in the fusebox. On my 300E, there are more than a few locations. Been there, as they say. Another $7 to $8 bucks and 15 minutes well spent.
Good luck and welcome to the forum.