You need to look at the basic state change example in the IDE. But instead of turning an LED on an off, you send a MIDI note ON message when the button is pressed and a MIDI note OFF message when it is released.
You will find life so much easier if you use Hexadecimal notation for your message numbers. For example 176 in decimal is B0 in hex. To write a number in hex then use the prefix 0x -
Would be the pitch bend message.
The messages you want to send are:-
Note On is 0x90 and note off is 0x80
It looks like you, or whoever wrote that code, might be dyslexic, I am too and I recognise that extra 'e' in the function name as a mistake I would make. It just need to be sendMidi