Original report: https://forum.mattermost.org/t/ios-select-avatar-issues/5961
If Mattermost doesn't have permission to the photo library because the user denied the first prompt, the app should prompt to give permission to send the user to settings app to manually change the permission.
"Mattermost Beta" would like to access your photos
Upload photos and videos to your Mattermost instance or save them to your device. Open Settings to grant Mattermost Read and Write access to your photo library.
[Don't Allow] [Settings]
Don't Allow: Dismissed modal and no change in permissions
Settings: Takes user to the settings app at the appropriate screen to adjust permissions for Mattermost