Nikon D780 DSLR Camera (Body Only) - Manual (Page 149)

103 Camera Controls
Adjusting Flash Compensation
Hold the N ( Y ) button and rotate the sub-command dial.
• Choose positive values for brighter lighting, negative values to
ensure that the subject is not too brightly lit.
• Normal flash output can be restored by setting flash
compensation to ±0.0. Flash compensation is not reset when
the camera is turned off.