If an app is not prompting you to select new photos from your gallery, here is how you can reset its photo permissions
Go to Settings > [app name] > Photos
From here you have two choices:
A)If you wish to grant the app access to all photos, select All Photos. When you switch back to the app, you will see all photos available.
or
B) If you wish to control the photo selection available to that app:
-Change Allow Photos Access setting to None.
-Back out one step from this settings page to return to the app’s settings.
-Go back into Photos and change the Allow Photos Access setting to Selected Photos.
When you switch back to your app and attempt to import a photo into it, it should now prompt you to add more photos to the selected photos made available to that app.