2006 Mercedes-Benz C230 stuck in 1st gear??

well must have been one hard hit..you have jarred one of your TCM fuses lose or blown if theres no underneath damage or fluid leak you jarred a fuse or trans relay to lose contact but sounds like a blown fuse you have 3 fuse panels for that type car get a test light key on test both sides of the micro fuses and push them in with your finger to insure good contact your main relays are under the hood push them down as well plastic loves to jump...lol

so i can do this myself and the "check engine" light will turn off and the car will revert back to normal?

if the car is in limp mode does check engine light come on?

There are altogether 4 reasons for that. No.1 transmission fluid level either too low or too high. No.2 there is a fluid leak. No..3 conductor plate faulty or soaked in oil due to leak n No.4 there isn't enough electricity reaching ur transmission