There's currently a bug in iOS Gospel Library where downloaded media doesn't get removed when books in the library are removed. If you've downloaded a lot of audio and video files in the past that you no longer use, you could try deleting and reinstalling the app to start fresh. (If you use annotations / notes / highlights, make sure that your latest annotations have been backed up / synced before you delete and reinstall the app. As long as you're signed in with your Church Account, your data should be backed up, but you can verify by checking for your recent annotations on the Church website or other devices with Gospel Library.)
Samuel Bradshaw • If you desire to serve God, you are called to the work.