Nikon D780 DSLR Camera (Body Only) - Manual (Page 431)

385 Playback
The Playback Menu
The [ Delete ] item in the playback menu contains the following
options. Note that depending on the number of images, some
time may be required for deletion.
Option Description
Q [ Selected ] Delete selected pictures.
i [ Select date ] Delete all pictures taken on a selected date ( 0 387).
R [ All ]
Delete all pictures in the folder currently selected for
playback. If two cards are inserted, you can select
the card from which pictures will be deleted.