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.

Helpful. Thank you.
Good help :)
getting this error:
(XID vmtrz8) Sorry, the domain is already pointed to an IP address that does not appear to use DNS servers associated with this server. Please transfer the domain to this servers nameservers or have your administrator add one of its nameservers to /etc/ips.remotedns and make the proper A entries on that remote nameserver.