Simple, navigate to SSL/TLS option in cPanel and you will see this:
Then click on Manage SSL sites. and you will see a list and your domain also a description about the SSL that is installed, in this case SelfSigned. Click Uninstall/Delete and you will get rid of it.
Next thing, you want a SSL for sure; go back to cPanel and go to SSL/TLS Status option. From this point you can AutoSSL all the domains that you have in cPanel. It will basically install certified SSL for your domains.
I hope this helps.