Omnibus F4 v4 voltage telemetry


I am a nubee building my first drone and will be using an omnibus f4 v4 (purchased from and an x8r receiver. I was also planning to power the FC through a UBEC. FC is flashed with iNav.

Would anyone be able to guide me on what I need to do to have voltage (of the main battery pack, not voltage after ubec) telemetry please?