To change the email address of your Withings account, please follow these steps:

1. Navigate to the Online Dashboard.
2. Click your avatar in the top right corner and click Settings.
3. Select Update email.
4. Enter your new email address twice.
5. Click Modify.

You will then receive a validation link in your new email address. Please note that after clicking on the link you need to log in with your old email address before the modifications are taken into account.

Note: You can only change your email address if you log in using your email and password; it won't work using Google Sign-in or Apple ID, as the option won't appear.