Per the manual.

�� GTLVREF Lane 0
This function defines the voltage level for GTLVREF Lane 0. Use the Page
Up and Page Down keys to select a voltage or select [Auto]to automatically
set the voltage.
�� GTLVREF Lane 1
This function defines the voltage level for GTLVREF Lane 1. Use the Page
Up and Page Down keys to select a voltage or select [Auto]to automatically
set the voltage.
�� GTLVREF Lane 2
This function defines the voltage level for GTLVREF Lane 2. Use the Page
Up and Page Down keys to select a voltage or select [Auto]to automatically
set the voltage.
�� GTLVREF Lane 3
This function defines the voltage level for GTLVREF Lane 3. Use the Page
Up and Page Down keys to select a voltage or select [Auto]to automatically
set the voltage.