If you have made some attempt to get this going then you should post the code here. Then we can help.
Have you written and tested a program to read the MIDI into the transmitting Arduino? And a program to send it out from the receiving one?
How about simple programs to send any old data over RF, receive it at the other end and just print it to check it's transferring o.k.? Something like the examples from nRF24L01 tutorial or another tutorial or yet another
Once you have those working you're almost there.
Steve