Is there a way to take an mp4, 28 seconds long, and set it as my new ringtone using GarageBand?

In the past, I was able to go into garage band, create an audio track <30 seconds, and click "export as ringtone" or something like that. I no longer see the "export as ringtone" option. Is there a way to take an mp4, 28 seconds long, and set it as my new ringtone?

[Re-Titled by Moderator]