If you wish to change the visibility settings of all the photos and videos that have been uploaded, you can do it from "Change All Visibility” under the Settings tab.
We are looking to offer more ways to customize visibility in the future, such as the ability to change the visibility settings of a selection of photos/videos or assign multiple photos/videos to a Share Group at once. However, it may take some time for these features to become available. We appreciate your patience and understanding.