You can modify the shape of a boundary that you saved to your Hunt Area when you visit the Mapping page on the HuntStand website, not the HuntStand app. Click MODIFY MAP FEATURE (pencil icon) > MODIFY. Left-click once on the boundary you wish to modify. Move the orange dots that appear on the saved boundary to modify its shape. This action cannot be undone. You do not need to click a save button. Simply click SELECT (hand icon) to deactivate the Modify tool.
Be sure to sync your Hunt Area! You must sync your Hunt Area on the app so that you can back up and view the changes you made on the website. All syncing is initiated on the app. While you have a strong Wi-Fi or data connection, tap the Current Hunt Area banner at the top of the screen to view a list of your Hunt Areas. Tap the Sync button (The button looks like circular arrows.) next to the name of the Hunt Area you'd like to sync. Check out this brief tutorial video on syncing.