You can do this from Gospel Library's app info page in Android Settings.
Depending on your version of Android, it will probably be in one of these places:
- Android Settings > Application Manager > Gospel Library.
- Android Settings > Apps > Gospel Library.
- Android Settings > Apps & Notifications > App info > Gospel Library.
- Tap and hold the app icon and select "App info."
On the info page, tap "Set as default."
Next, tap "Go to supported URLs" (or "Open supported links") and choose what you want to happen the next time you click on a link to a general conference talk or scripture.