Domain Aliases are additional domain names that can be set up to point to one of your sites. For example, example.fr and example.de can both point to example.com.
Go to "Websites & Domains".
"Show Advanced Options" if they are hidden.
Click "Domain Aliases".
Manage the aliases for each domain by clicking the appropriate link.
Click "Add Domain Alias".
Type the domain alias name.
Click "OK".
That's it! Now the alias has been set up and can be managed or switched off here.