Within Teamwork, you can mark any of your projects as complete in the project's settings.
Hover beside the project name to reveal the options button. Click the three dots and select the Complete option within the Manage Project section.
You can also complete a project via the Dates section of the project details pane on the left of the Overview section of the project. Click one of the existing dates or select the Edit option.
In the project dates modal, you will see an option at the bottom to mark the project as complete. Click Set Project Dates to save the changes.
The project details sidebar in the Overview tab will be updated with a note of completion.
Note: Completing tasks and milestones will not automatically complete a project so you need to mark the project itself as complete.
For more information, see: Completed Projects