how to get project linked without previous account info

Permalink 1 user found helpful
I can't find a tutorial or contact information on how to deal with this.

We are running 5.6.2.1, and I need to install an add-on, but cannot.

The current error when trying to do anything with the concrete5 community is:
The base URL of your site does not match a registered instance of the site.

which leads to a need to log in with an account that is associated with the project. I cannot tell if:
A) there IS an account on concrete5 that is linked
B) whose it would be

In either case, any of the previous people who would have made linked accounts are no longer in the group. Any help on how to move a project to my account without access to the previous administrator's account info?