This unlocked near the end.
Throughout the game choose blue and silver tide choices in dialogue.
Complete Aligerns quest which starts at the valley by visiting a monument, complete this quest in the bloom by stealing the black frame from the Murden Vault and giving it to Orth.
Now at the end of the game during your final confrontation with the Spectre convince him he isn't the real changing god. Upon his realisation and only provided that you have made similar choices to the changing god he will offer to merge himself into you, thus you become the changing god.
Once this occurs ALIGERN will ask to talk to you. Do so and he will forgive you for destroying his village.