You can easily view what offers have been created for your Groups and have the ability to delete an existing offer and/or create a new one right from within the Group.
Navigate to the Groups tab on the left-hand side to view your groups. Once you have clicked into the group you want to edit an offer for, click on the 'Offers' sub-tab.
This will display your current offers for that group. You can easily delete an offer by clicking on 'Delete'.
Note: When replacing an existing reward, remember to delete the previous reward first then add the new one.
To create a new offer for that group, simply click on 'Create Offer' which will take you to the Triggers tab.