To unlink a GitHub pull request from a Xebrio task, go to the details window of the specific Xebrio task. Navigate to the GitHub tab, and then to the Pull Requests secondary tab. For the GitHub pull request to be removed, click on it's three dot vertical menu and select the Unlink Pull Request option.
Users will need view and edit permissions in the tasks module to perform this action. Depending on the user's project permission settings, they may be able to view all project tasks or just a subset. Watchers specifically added to the task will be able to view it.