professional / cPanel.

You can access cPanel by calling the url domain.com/cpanel

If you are looking for cPanel server management we can assit you with this https://iserversupport.com/cpanel-server-management/

They want $30 before they will even talk to you about the problem.
SLACKSCRIP setup cPanel for me. I could not login with the root password, even though I could SSL into the box, change ~/.bashrc, then exec bash after adding

export PS1="[\u@\h \W \@]\$"

So, this was a script error. after telling them 4 times the password was the problem, they finally realized, it was a password problem.

i believe that stackscript is for paid managed linode users only

There's nothing at all special about that stackscript that would preclude a non-Managed customer from using it, but you're going to need to bring your own license as Linode does not provide them, except as a part of Managed.