How can I create custom ringtone for FaceTime on MacBook Air?

Re: I can't seem to find any way to make my own ringtone for FaceTime on my MacBook Air 13, are there any suggestions to help me?

Wondering if this User Tip from a respected Community member can help you:

Create and manage ringtones - Apple Community

For FacetTme: You can choose a ringtone for any particular contact in the Contacts app;

See how to: Update contact information in Contacts on Mac - Apple Support