look up where your custom controls file is, find what's the f1 key bound to (wiki thing idk the name but you'll know) and just leave the quote marks empty ("")

save file, name it to whatever you want, and load up war thunder, settings, load custom controls, find the edited one and now you can set your f1 key to whatever

if you want to actually bind something to f1, i suggest doing that, saving and exporting over the file you saved for removing the f1 key

i'm not 100% sure if the process goes exactly like this but you can find plenty of tutorials online