Offers will come off the app automatically on the date specified when adding it. If it is one that you added yourself, you can remove it early if needed. When you go into the ‘Add an offer’ button you will see a list of offers that you created. Here you can edit any offer or simply remove it.
Press the ‘Add offer’ button then on the next screen the blue bar at the top. You will also see in the Add Offer button a list of your present offers.