Ensure tips are firmly installed on the device. After installation, quickly compress the tip with your thumb and forefinger, insert and hold the device in place for a few seconds while the foam comfortably expands to fit your ear canal.
Installing tips onto your earphones and inserting tips in your ear canals is easy. Check out this video.
If you notice the high frequencies "rolling off", please follow the steps in this video from InnerFidelity: