How to edit a tone on iPhone 8plus?

How do you edit the starting point for a tone purchased in iTunes directly on your phone?

In the olden days, on your Mac you could edit the stating point by clicking on "song info" go to "options" and select a start and stop time. But now that "tones" are not supported in the iTunes app on the Mac, how can you edit the start time for a iPhone tone on the phone?

Thank you kindly.