Private projects can only be viewed by those who are a contributor. If you have the URL of the private project because you were supposed to be added as a contributor, or the owner of the project shared the URL with you, you can request access to the project.
Navigate to the project using the project's URL.
You will be taken to a page that says you need permission to access it.
Click the green Request access button. Or, if you are already a contributor on the project, but you are logged in to the wrong account, click the Switch account button.
The button will become disabled, indicating that your request has been submitted.
The admin(s) on the project will be notified via email that you have requested access.
If the admin(s) grant you access, you will be notified via email that you have been added as a contributor to the project.