Hi guys,
There are many tutorials for FCC mode using Fake GPS app, but those methods ask you to turn off the data or turn on the airplane mode...
and sometimes those methods are not working... so here's simpler tutorial for you guys.
Initial Setup:
1. Turn on FakeGPS(set to US)
2. Run FreeFlight6
3. Force close FreeFlight6 after you see the main screen
Continuous use:
1. Turn on FakeGPS(set to US)
2. Connect/turn on the controller(FF6 will be automatically run)
3. Turn on Anafi
4. Set channel to 36~165
5 Turn off FakeGPS
6. enjoy
7. Force close FreeFlight6 after you enjoyed your flight
here's youtube tutorial:
(I'm South Korean, so please don't say about my English skill

)
For your information,
"Force closing the app before disconnecting the controller" is the most important part of this tutorial.
The app has 2 important program methods that interrupts your FakeGPS tries.
"onDisconnected" method clears all your preferences stored in the application data including CountryCode
"onCountryCodeChanged" method sets your drone's wifi output mode(FCC/CE) based on your real location information(maybe GPS, wifi, bluetooth, IPs...)
If you disconnect first, the stored CountryCode will be "null"
If you force close app first, the stored CountryCode will be "US"
and after running the app, the app will compare the stored CountryCode and your current CountryCode(which is "US" with Fake GPS), and if both are same, then onCountryCodeChanged will not be run.
If both are "US" in the initial process, the app will choose FCC.
In order to bypass those 2 methods, you must force close the app before disconnecting the controller.