Press and hold on your calendar or on a snippet in iOS and 1SE offers a menu of quick actions. What you get depends on what you press, and the actions are grouped under headings.
An empty day
Under Go: Previous empty day jumps back to the last day with nothing on it, Back 1 month and Back 1 year move the calendar, and Go to date opens a date picker.
A Fill heading with Autofill appears as well when your library holds a photo or video taken on that day.
A day that already has something on it
The same Go actions, plus Playback > Mash day to mash everything on that day, and an Edit heading with Clear and Delete. If the day holds more than one snippet you also get Snippets > Reorder Snippets.
A single snippet
Open the day first, then press and hold the snippet itself:
Replace: swap in a different photo or video
Post to Project: copy the snippet into another project
Make Private: keep the snippet out of your mashes
Delete: remove the snippet
Share, Edit and Change Caption aren't in this menu—they're buttons under the snippet on the day screen.