Okay, so I will try to help you by explaining how I solved it. I don't play piano but I know how to read solfege which is what the green heart's hint is.
The solfege syllables are as follows: do re mi fa sol la ti do. The bigger symbol on the left is a treble clef. The line where the first note starts is the one the treble clef wraps around.
That line is the solfege syllable 'sol'. The next is 'fa' then the last is 'do'. After figuring this out, I looked up "solfege piano notes" on google images. Which translated the solfege to the corresponding piano notes. Which are G, F, and C.
Then I go look up "piano with notes" labeled. From there look for the notes G, F, and C. Then click on the notes in order on the piano in game.
If you need to figure out where they would be on the piano remember the amount of black keys between notes(2 and 3). If this didn't clear things up let me know, and I will try again to help you. :)