Help Please - how do I activate the program?

Make sure to run a malware scan on you computer, as pirated or illegal copies usually contain malware.

We cannot offer any help since you had gotten the program illegitimately. YouTube is filled with videos promoting software piracy. In addition, the download link was for a version of Premiere Pro CC (typically, the 2017 and earlier versions) that is no longer "authorized" for use by legitimate Creative Cloud subscribers, and therefore can no longer be activated at all. As such, you should report that to YouTube instead of asking us for help.

Go through the proper channels.

https://www.adobe.com/products/premiere/free-trial-download.html

>through a link given on YouTube

That is not how you get Adobe programs

Cloud Manager to install all programs https://www.adobe.com/ie/creativecloud/desktop-app.html
https://community.adobe.com/t5/get-started/how-to-activate-your-adobe-software/td-p/9636861?page=1

You posted this in the Captivate forum, will try to move it to the Premiere forum.