Ble keybord - how to connect it and use it in MIT app?

hi, I need to connect my app with physical buttons, unfortunately still can't make it work with regular bluetooth way, to send data by serialBT from arduino,

but maybe better way is to use blekeyboard commands, like PREV>, STOP> ect.
I use ble keyboard code by arduino to connect to one of android app (map roadbook),
and there is possible to deal with functions in that program, but it's ready to work app (not main ;), and have no idea how to set it)