reset from key 2003 v220 cranks wont start!

[Indiana1917]

mercedes v220 2.2cdi 2003 left battery off overnight to charge
i know i can reset from the key but not sure how i do it?
the engine cranks but wont start never had a problem in the past always started first time
not the battery i have tried a few same issue
starter motor is also fine
immobilizer?

 

[mioba]

I would say you have a fueling / ignition issue if its cranking.

 

[Indiana1917]

I would say you have a fueling / ignition issue if its cranking.

i have had it before had to do something with the key but cant remember what the process is