Nikon D3300 - Manual (Page 140)

120 P, S, A, and M Modes
Flash Compensation
Flash compensation is used to alter flash output from the level
suggested by the camera, changing the brightness of the main
subject relative to the background. Flash output can be
increased to make the main subject appear brighter, or reduced
to prevent unwanted highlights or reflections (
0 347).
Keep the M (Y) and E (N) buttons pressed and rotate the
command dial until the desired value is selected in the
viewfinder or information display. In general, positive values
make the main subject seem brighter while negative values
make it seem darker. Normal flash output can be restored by
setting flash compensation to ±0. Flash compensation is not
reset when the camera is turned off.
M (Y) button
+
Command dial Information display
E (N) button
–0.3 EV +1 EV