To delete an entry in the Mac app:
Right-click (Control+click) on the entry in the timeline, and select “Delete” in the context menu.
With the entry open in Read view, tap the More icon (•••), then select “Delete” in the context menu.
To delete a photo in the Mac app:
Open the entry.
Right-click or Control+click on a photo
Choose Remove Photo
To delete an entry in the iOS (mobile) app:
In the Timeline view, swipe on an entry.
Tap Trash icon and confirm
While viewing an individual entry
Tap the date at the top or the map at the bottom to open the Metadata view
Scroll to the bottom and select “Delete”
To delete a photo in the iOS (mobile) app:
Long press on any photo