A Test Plan tracks a group of Tests, regardless of the number of Test Executions for a given version. Test Plans may be used to group the Tests in the scope a given sprint and thus, consolidate the test results.
Make sure that the agile board scope includes Test Plan
Check the Agile Board Filter and confirm the issue type "Test Plan" is included.
Review details at the step Setting scope for the Agile Board, from this module.
Add the Test Plan Status Field
Go to the Project side Bar > Select Backlog or Active Sprint > Board > Configure.
Click the Card Layout and add the Test Plan Status to the Active Sprint.
Check the result
When you include the Test Plan Status custom field, you are able to see right away the overall progress of your Test Plans.
Typically, you will have a Test Plan per sprint, like in the example. But if you want you can create several test plans in your sprint.
Note that you are limited on the number of fields (3) you're able to include in each card on the board.