Take the ZERO II 

see picture ZeroII-Switch.jpg

1. Remove all power and connections form the ZERO II

2. Remove the yellow tape from the Slide switch 
3. Slide the Switch DOWN towards the USB power 

4. Start the RigExpert Flash Tool v1.6.1.exe

Plug in the Zero II into USB 

Select update from LOCAL file 
Select the file   

fw_ZeroII_ver_1_0_38400.bin

click Next button to flash it 

record your "Serial Number" to verify the ESP32 code works !!!

5. Move the Slide switch to external power
power from 5 Volts not 3 or 3.3volts