In the Capture view, tap on the current frame rate setting (FPS) then select Capped at 240 fps. Swing Profile will then choose highest possible frame rate for your device (see Hardware and Software Requirements). The highest frame rate achievable by Swing Profile is 240 fps on iPhone 6 and iPhone 6+.
Note that recording at high frame rate requires slightly longer wait time to write the video file after capture (a few seconds more) and larger storage space for the video.
