DA 40 NG - Diesel option OAM 40-370
You can easily find this out for yourself by searching on the OAM.
This leads to Diamond Aircraft service bulletins relating to the change.

Work instruction

AFM

Software notice

Looks from these that it requires 3 things:
2 placards relating to the different engine operation temperatures, and potentially a software upgrade to the engine management system (depending on the version currently installed).