Before adding an Addon Domain name you need to point your addon domain name server to your main domain name server and you will need to wait for domain propagation. It usually takes between 12 and 24 hours.
1. Log into your cPanel account.
2. In the "Domains" section, click on "Addon Domains" Icon.
3. Under the "Create an Addon Domain" option you should enter your addon domain name, username, and password.
New Domain Name: Your Addon domain name like example2.com
Subdomain: It will be automatically filled in by cPanel.
Document Root: It will be automatically filled in by cPanel.
Password: Enter a new password or use the "Password Generator" button.
4. Click on the "Add Domain" button.
If the domain is successfully added, you will receive a message like this.