problem with the key "fn" on the evo80 keyboard

[ngotchut]

I use evo80, my first own keyboard and I tried via app. However, I have assigned the button "Fn" to another function so I cannot press the function key combination. And I can't switch back to wired mode to access the via app. right now it's on bluetooth mode.
How can I back to the default, please help, thank you so much.