When creating a domain redirect, you have two options.
If you are simply pointing domain1.com to domain2.com, you can use the in-built "Site Redirection" feature.
Simply create a new Redirect and enter the new domain.
However, if you need to create a domain redirect where domain1.com/login needs to point to domain2.com/login (and any other directory/file beyond the top level domain), then you can use a .htaccess file instead.
Go to "System Info & Files", then click "File Manager" - find the domain that you want to create a redirect for.
Right-click and press "Create File"
Name it ".htaccess" (the leading dot is important)
Within this file, paste the following code (replacing the original/destination domains with your own).
RewriteEngine On
RewriteCond %{HTTP_HOST} ^domain1\.com [NC]
RewriteRule ^(.*)$ http://domain2.com/$1 [L,R=301]
If you require any assistance, please contact our support team.