There’s a solution posted on the developer’s website. You guys can try it so you don’t have to sacrifice all the work that’s been done on your site.
1) creating a New Admin in my PHPBB so it would make one on the WP side. (Despite what these guys say if you have used this previously as I have once you update it, it stays active and the widget does not.)
2) Make the New User a founder and a n admin on the WP side.
3) FTP into your WP-Content folder and rename the phpbb Bridge temporarily so you can have admin access to the Dashboard.
4) Login as the freshly created Admin and remove your old admin account. (Don’t forget to give ownership of your posts to the new admin.
5) Rename the PHPBB Bridge folder back to normal name and activate in the Plugins and widget areas per the instructions. In my case the New admin DID have access to the Admin/Dash. Now the bridge should be acting normal again and you can logout of the new admin account. Go to phpb and login as your Main admin account and the bridge “Should” remake the user in WP. you will need your new admin account to make your old one a founder and admin again and you can reclaim your posts.