It is in pg 72/73 of manual under transmitter/Air Integration menus
T1/T2 Setup
The T1 & T2 menu pages allow setup that is individual to each transmitter/tank.
Serial Number Setup
Every transmitter has a unique 6-digit serial number. This number is etched onto the side of the transmitter.
Enter the serial number to pair the transmitter to T1. This number only needs to be entered once. Like all settings, it is stored in permanent memory. Transmitter settings are saved across all dive modes.
Reserve Pressure
Enter the reserve pressure
The valid range is 28 to 137 bar (400 to 2000 PSI).
The reserve pressure setting is used for:
1) Low pressure warnings
2) Gas Time Remaining (GTR) calculations
A "Reserve Pressure" warning will be generated when the tank pressure falls below this setting.
A "Critical Pressure" warning will be generated when the tank pressure falls below the larger of 21 Bar (300 PSI) or half the reserve pressure.
For example, if reserve pressure is set to 48 BAR, the critical warning will occur at 24 BAR (48/2). If the reserve pressure is set to 27 BAR, the critical warning will occur at 21 BAR.