This is an easy one. Go to DH main menu, click on "manage domains." You will see a list of all your domains. In the column "web hosting" for the domain you want to redirect, click on the wrench icon. In my case, the word "fully" is next to the wrench on all my domains.
once you get to the page controlling that domain, go down the page to where it says "redirected" and put in the URL you want to redirect to. Click the "redirect... " button.
Piece of cake