If the app stalls whilst loading or will not open at all please first try restarting your device. If the app is still failing to load then you will need to uninstall it, restart your device, and then reinstall then download it again from the App Store.
To delete an app, hold your finger down on the icon until it begins to wobble with a small cross in the corner. Tap this cross to remove the app from your device.
Once reinstalled you can restore your previously purchased subscription and access all your packs. To do this, open the reinstalled app, tap on More > Settings > Restore Purchases, and all the recipes will all appear in a couple of minutes. Unfortunately, reinstalling does mean if you have any recipes marked as favourites this information will be lost and you will need to remark them.