Did you verify that you have the correct KD8CEC code? If so, then you can enter the BFO value in the USB Calibration field of the Memory Manager and then write the values to the ubitx Nano.
Above is a screenshot of one of my early v5 calibration settings. All of my ubitx are in surgery, so I cannot get a clean capture of current values.
1 - Need to read and write the values from the ubitx each time.
2 - The values are not used until you reboot the ubitx Nano. This includes removing the power from the USB cable.
(be sure to disconnect by pressing the changed connect button before removing the USB cable, otherwise, you will need to close and restart the Memory Manager program)
3 - It is best to save values between trials to a file, renaming the file save location each time (i.e. Trial1, Trial2, ...)
4 - Since this capture, I found out that you only need to enter the USB Calibration, the LSB is not used and should be 0
The zero beat for frequency calibration is to be done against an AM station that you can receive and know the frequency. Most in the US can get one of the WWV frequencies, 5 MHz, 10 MHz, 15 MHZ, or 20 MHz.
The BFO setting is through the "noise" on a frequency without a signal. You do need to connect to an antenna for this test, AND you need a microphone connected to your PC and use the Chrome browser for the BFO Tuning Aid to work. What you see in the video from Ashhar Farhan is the noise "plateau" from a clear frequency.
If you cannot receive any of the WWV frequencies, then you can also us an AM station, as long as you know the exact frequency, and you take the time to tune down to the frequency on the dial (There is a shortcut direct entry on one of the KD8CEC screens).
Hope this helps