Sony FX 6 Quick Start Manual page 62

Exposure: Changing GAIN and ISO in smaller increments
The L,M,H switch provides an easy way to change your GAIN
or ISO in presets but you can also change in smaller
increments using the direct menu.
The ISO/GAIN button on the side of the camera will allow
you to adjust in smaller increments in the direct menu.
The GAIN or ISO rating will highlight in the display.
This actually changes the preset setting for whatever preset
you are on at the time of the change: L, M or H.