How to set permission to all photos?
There has been an issue with iPhone before which could cause this issue for you.
Please uninstall and reinstall the Relive app. You will not lose any data by reinstalling your app. After the reinstall you should be able to select All photos. It might help to restart your phone after the reinstall, before heading to your settings.
The photo permission can be changed from your phone's settings instead of within the app:
Open the Settings from your phone
Scroll down until you see Relive and click on it to open
Tap Photo's and select All photo