How do I add my personal CCaccount to my secondary Professional CCaccount ?

You cannot merge, add, or combine accounts. You cannot use apps in different accounts at the same time. You might consider whether you want to move entirely to using a single account. If you do want that, Adobe Customer Service might be able to help. Though it might need permission from the business admin. Or it might be impossible.

I don't think there is any way to add an app from one account to another. The only way that it can work is have all the applications installed on the computer and switch the account when you need to use the application purchased on the other account. You can contact support to get more information. Login to your account and navigate to the URL below. Make sure that the browser has cookies enabled, and all script blockers are disabled.
https://helpx.adobe.com/contact.html?rghtup=autoOpen
Type AGENT to avoid bots and talk to a human.
Also, be mindful of answering anyone who sends you a private message. See the following for more information about scammers
https://tinyurl.com/y7cfrr7y
-Manan