Yes! At any time you would be able to repeat a session or a pack from earlier on in your Headspace journey.
Simply tap on the desired pack under “My Packs” from your Home screen, or tap on the “Discover” icon and select the appropriate pack. You can scroll to the left or right until the session appears in order to play the particular day/session. You can also tap on the “information” icon indicated by a lowercase “i” to Restart the entire pack with all sessions locked.
Repeating packs and sessions is all part of the Journey and experience of getting the most from your meditation practice!