The new experiment features a slider above the navigation bar between “All Photos” and “Memories” in the Photos tab. When you switch to Memories, you’ll see a feed with photos of certain events presented as collages with different frame shapes.
Clicking on them will open the usual interface of memories in the form of stories. There’s also an option to rename memories by long tap or a special ‘Edit’ button on the top right.”
For now, this is an experiment and is not available to users.