The Holodeck allows for easy navigation of all the campaign stages allowing you to see more information, replay them at different difficulty settings, get achievements, or just experience them all over again!
How to use the Holodeck
From the Map, tap the Holodeck icon on the top left.
You'll find a list with all the planets you already completed.
Check the rank marks the max difficulty that you completed on a planet
Scroll to find your desired planet and tap it. Hit PLAY to replay the stage.