You can only change the email ingame if your acclunt isnt verified. Youd have to contact support requesting a change at this point.
See I have this account I want to sell (6/8 Mystic) and I noticed with the verification policy you can change the email you signed up with. But my mystic account was verified previously so it will not give me the prompt. Is there anyway I can force this prompt or access it? If so PLEASE tell me in comments ^^.
You can only change the email ingame if your acclunt isnt verified. Youd have to contact support requesting a change at this point.