The Command Dials - Nikon Z fc N2016 Reference Manual

To select [X] or [T], or to change from [1/3STEP], [X], [T], or [B], rotate
while pressing the shutter-speed dial lock release.
1
1/4000 s–1/2 s
2
1–4 s (red text)
3
B (Bulb) (0134)

The command dials

Rotate the command dials to choose settings for aperture or the
functions assigned to other camera controls.
Camera controls
4
T (Time) (0134)
5
X (Flash sync) (0361)
6
1/3STEP (1/3 step) (0130)
48