I just found it.

# fast-gpio set 15 1 #B
# fast-gpio set 16 1 #G
# fast-gpio set 17 1 #R

If you want to turn it on,

# fast-gpio set 15 0
# fast-gpio set 16 0
# fast-gpio set 17 0

Is there any way to turn off Omega Expansion Dock LED?

I just found it.

# fast-gpio set 15 1 #B
# fast-gpio set 16 1 #G
# fast-gpio set 17 1 #R

If you want to turn it on,

# fast-gpio set 15 0
# fast-gpio set 16 0
# fast-gpio set 17 0

Is there any way to turn off Omega Expansion Dock LED?

@Pedro-Baco Good to hear. I tried to use i2cset and i2cget, However, the module returns nothing... I can see the module on i2cdetect. Could you give me a some advice for it?

@Boken-Lin Could I test the OLED screen with i2cset? I want to check that the module is working or not.