After listening to the song, hum the first note and try to find it on your instrument. If you have to, listen to the opening of the song on a loop a few times until you manage to find the first note. Once you find the first note, write it down.
Is there an app to identify piano notes?
The Note Recognizer analyses the pitch frequency that you sing or play, and gives the corresponding note name. Very useful for singers who need to find the right starting note of a song. Or if you want to know the key of a song; sing the tonic, and you get the note name of the key.