I figured it out. I hope this works for you. Note I have only tested this once as I am not brave enough to test it twice:
- go to https://app.circleci.com/projects/project-dashboard/github/YOURORG
This page should stay in the new UI and not redirect - click “Set Up Project” on a repo that isn’t already building. This can even be a new empty repo.
- Click Start Building
- Click Add Manually
- Click Start Building
That’s it. your account should now be forced back to the new UI mode
If you want to undo the builds for the project you just used, click Project Settings->Stop Building