1. Log into your server using RDP.
2. Click on Start, administrative tools, and then Internet Information Services (IIS) Manager.
3. Click the plus sign next to your server to expand it.
4. Click on the plus sign next to site to expand it.
5. Right click on the site you wish to add the binding or alias to and click on Edit Bindings.
6. Click on the Add button.
7. Here you can select the type either HTTP or HTTPS if you are using an SSL and then select the IP address associated with your site. Enter the domain name that you wish to be an alias for the domain that you right clicked on and hit ok.
8. Repeat steps 5-7 except use www.example.com (replace example with the domain you want to add as an alias for the domain you will right click on) as you most likely want to include the www subdomain as an alias. (if you are adding a subdomain such as sub.example.com you will only need to do steps 5-7 once).