Visit Grey's website
Click on 'Trouble signing in?'
Click on the option "I want to change my email."
Type your current email address
Enter the verification code sent to your old email address.
You can click "Send to linked phone number" if you don't have access to the email address.
Type your new email address
Enter the verification code sent to your new email address.
After this, please complete the KYC, and the new email will be updated once it is verified.