How do I use ringtones as text tones on MacBook Air?

Why can’t I use ringtones as my text tones? I need my loud n long twinkle, the other text tones are too short & not loud enough. Please bring back this feature. I can still do it on my MacBook Pro but I can’t on my new Mac air book, but in my MacBook Pro it won’t transfer. I see a lot of people complaining about this being it back! It should’ve never been changed.

[Re-Titled by Moderator]