Connect Flipper to PC
Open Putty
click serial 
Connect to flipper COM port at 115200 speed
Help  to display commands.

CLI = Command Line Interface
putty.exe -serial COM3 -sercfg 115200,8,n,1,N

Commands to use in serial
help
storage list /
storage list /ext
storage read /ext/badusb/demo_macos.txt
storage write /ext/badusb/rootjunky.txt
paste in file data or type then CTRL + C to close and save. 
storage remove /ext/badusb/rootjunky.txt
loader list
power reboot2dfu
power reboot
power off
power debug
factory_reset
device_info

Encode in LF not CRLF window ending.
Edit tab then EOL conversion in notepadd++

https://flipperzero.one/update

https://update.flipp.dev/