I found this by accident.
Tutorial:
Loading a save or starting a new chapter
go to the console and enter sv_cheats 1
then write god
as soon as it says that you have received a message that you have immortality, then save the game and then go to the menu
Open the console in the menu and write sv_cheats 0
Then load your save
Ready!

Now you are immortal, and as a plus you have the opportunity to receive the achievement