This article applies to the 123-reg InstantSite package.
This article will explain how you can add a Forum page to your InstantSite.
Scroll down to the Create your website section and click on the InstantSite icon.
Click on the Login button next to the relevant InstantSite package.
Click on the Pages link.
Click on the check box next to the Forum and click on the > to move the page to your site structure.
Click on the Save Changes button.