How do I share an existing album?
You do have to create a new shared album, but you can create the album from the contents of the existing album so you don't need to find the images again manually.


Open the album.
Choose Select in the top right, then Select All in the top left.
Tap Share in the bottom left, then create a new iCloud Photo Sharing album as usual.


Once you've created the shared album, you can delete the old album.