anyone know how to reset the game to make the green balls spawn back?

If you're asking because of 100%, I've updated the rules recently suggesting to download the game. Download it from Gamejolt, because then collectibles (green balls) don't disappear if you have collected them in previous runs. Also the collectible achievement doesn't block the last orb in level 30 (which is more comfortable when retiming for the last frame).

If you insist on using the browser, even though I highly suggest to download the game for 100%, you can delete the cookies' folder. I use Opera, this is how it looks. Again, I don't recommend using the browser for 100%.