Bend the part that goes behind your ears a little more, it shortens them from back to front so they don’t slide down your nose. If they sit too high on the nose after that but stop sliding, you can spread the nose pieces a little so the glasses sit a little lower. (I need to pinch mine together more, usually, to get the rims off my cheeks, so ymmv.) Adjust as needed. It might take a few days of wearing to get them just right.