Open the Photos app
Go to Albums
Tap Recents
Tap Select
Tap and drag (or tap) to select duplicate photos
Tap the Trash icon
Tap Delete [number] Photos
Open Albums again
Tap Recently Deleted
Tap Select
Select the duplicates you want to permanently remove
Tap Delete All or tap Delete [number] Photos
To use iCloud Photos cleanup:
Go to Settings
Tap Photos
Turn on iCloud Photos
Wait for Photos to sync
Open Photos and check for duplicates under search results (if available)
Delete duplicates from the Photos app and then clear them from Recently Deleted