For what it's worth: smth = something in shorthand. I tried clicking on the link to help OP but it was dead.Hi Makash,
Unfortunately, I can't be of much help since I'm not sure what the "smth" button is or does and I don't even have a CLA yet.
That said, I'm not sure if you knew this already but you can actually access the CLA's owner's manual digitally from an Android or iOS device! Maybe it's just the geek in me but I think it's pretty neat!
You can also get it online at: http://moba.i.daimler.com/baix/cars/c117/cars/c117/en_GB/manual/index.html
I'm sure someone with actual hands on experience can help! Best of luck and enjoy your new CLA!!!