Occasionally, you may remove a project trigger for a specific use case but remove the wrong one erroneously. This can cause your project integration to fail and you will be unable to trigger builds as expected.
How Do I Add a New Trigger?
While there is no way to add the trigger back through the UI, you can try and navigate directly to
<orgID> with the organization ID from Organization Settings and replace
<projectID> with the project ID from Project Settings). At that point, you will be able to re-install the CircleCI GitHub App and create a new trigger.
For more information, you can refer to the GitHub App integration page.