If you go to your my.avast.com account and add the email you want to your list of emails. You should get a validation email (I think), once validated you should be able to change that to your default email. This I believe would then be your email address for the forum also.
You don't say what Avast Program your are using, Avast Free or one of the Avast Paid versions ?
The reason I mention this is, with paid versions your subscription is also linked to your email and that may be why you are being forwarded to your subscriptions page. What I don't know is how this could effect subscriptions linked to that other email.
