Inaccessible Files

I recently had to upgrade my MacBook Pro to MacOS Catalina 10.15.6. Before the update, I had all of my work files under a special tab under Favourites in Finder. This was set up in 2015. In the update, this file disappeared. The files are still somewhere on my computer but I can't get to them. There's over 400GB of data there, and though it is backed up to a hard drive, it is really causing an issue with storing new files. How can I find these and delete the little cretins? Thank you!