Toyota 2009 Tundra Owner's Manual page 408

3-4. Using the hands-free phone system (for cellular phone)
Setting voice guidance volume
Select "(GUIDANCE VOL)" by using
Change the voice guidance volume.
To decrease the volume: Turn
To increase the volume: Turn
Initialization
Select "(INITIALIZE)" and then "(CONFIRM)" by using
Select "(CONFIRM)" by using
384
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counterclockwise.
clockwise.
again.