The USB-C port is on by default. You do not need to press any buttons to activate.
Note: make sure the Omni Ultimate is powered on before plugging in your device and make sure you plug your USB-C cable into the Ultimate before plugging it into your device. Otherwise, your device might charge the Omni Ultimate.
Recharging from the USB-C port
USB-C port max input: 90W Fully recharge in under 3 hours
The Omni Ultimate can be recharged from most USB-C chargers. Simply plug your charger into the Omnicharge, and check the input wattage to see if it is receiving a charge.
If your Omnicharge is not recharging, first try to replug the USB-C cable. If this does not work try to turn off the Omnicharge before plugging in the charger. If the Omnicharge is turned off and charging, it will show a battery icon on the screen. You can then turn on the Omnicharge again if you wish to use it with pass-through charging.