use the circle tool and theres gonna be like a little menu in the corner when u start making the circle so when u put it in the place you want theres like a duplicate symbol so use that when ur finished placing one ear to make another that is the exact same size
and then just use the erasor tool to take a bite off of it
(theres a smooth line/stabilizer option for the eraser too, just look at the eraser settings if u want to get smoother circles)