Domain Mapping subsites of an Add-on Mulsite Domain

I finally found the answer.

When we use a subdomain (xyz.com) on the cpanel and create a wordpress multisite on it, we need to simply assign 123.com add-on domain in the cpanel and change the domain root to the same root of xyz.com. For example, if domain root of xyz.com is /public/xyz.com, then when we add 123.com, we need to use the same domain root /public/xyz.com also for 123.com.

Using same domain root as that of the main site in Cpanel, we can access 123.com as mapped domain for 123.xyz.com wordpress multisite.