In order to have more than one user with root privileges to handle WHM as a Reseller, there are several steps to take. You should login to your server via SSH and use these commands below:
usermod -aG wheel secondroot
echo "secondroot:all" >> /var/cpanel/resellers
Please take a note that "secondroot" should be changed into your wanted username. After performing the commands login into your WHM with root credentials and do the following:
Go to "Home";
Press on "Resellers";

- Then press "Edit Reseller Nameservers and Privileges".

Here check all the settings for the new user in ACL the same as your root user has:

After saving the settings, you can login with your new user via WHM