If you’d like to make a Gallery from your collection public or private, you can do this by selecting the Gallery and then clicking the pencil button on the right hand side of the screen.
Once you have done this, you'll be redirected to the galleries settings page.
If you want the gallery to be public select "Visible to everyone"
If you want the gallery to be private select "Only visible to me"
Once you have make the necessary changes, make sure you hit Save changes.