How do I get back Xylophone text tone on my iPhone 12?

Hey!

You can give this a try:

• Navigate to Settings > Sounds & Haptics > Text Tone
• Scroll down to "Classic" and go there
• Try out which one of the tones it is you're looking for! I suspect you mean the "Calypso" tone, but it might be a different one.

Xylophone is a ringtone. Prior to iOS 17, iOS allowed you to use ringtones as text tones. That is no longer an option. You'll need to either buy or create a tone.