Need to restore deleted account, but files were saved.

I deleted my regular years-old Thunderbird account by mistake (Oops!) , but I did not delete its many files, so they still show up on the left, and I can access the files, but the account does not send/receive emails any more. I understand why. I created a new account, but I cannot drag the old files into it.

Ideally, I would like to be able to make the deleted account work again … with its saved files, or else know how to transfer the files to the new account. Any guidance? Thanks, Tim I have enjoyed using Thunderbird for decades.