The easiest way to solve it is to do it one note at a time. Go to the organ and play the first note (low C). Hum that note to yourself, go to the control panel and move the first slider from the left until it matches the note you're humming.
Go back to the organ and hit the second note (Mid C), hum the note, go to the control panel, and set the second slider the same way. Repeat with the other notes. Then pull the handle.
It's even easier if you have someone else in the room to hum the note while you're trying to set the slider.
Another solution is to count the number of notes on the keyboard and
move the slider the same number. But this can be difficult if you have
trouble moving the slider a single notch at a time. [If you use Windows,
you can temporarily turn on the "Mousekeys" setting in the Accessability
Control Panel to make it easier to move a single note at a time.]
Go back to Myst Island -- Inside rocketship. Setting the notes.