If you use Spotify it will also give you the option to choose song from search as well clip and apply what part of track as alarm ringtone. If that helped please click the 3 dots on last reply and click solution accepted 🙂
If the above guide on how to change doesn't show or do what you are looking to do, it could be an issue and should be submitted to Samsung Members app as an error report. Reproduce the issue prior to submission, which in such case would be to look for ringtone setting, attempting to change, and observe either the setting is missing or not changing.
