How can I delete a ringtone that appears on iPhone but not iTunes?

I want to delete a custom ringtone; it appears on the phone but not on iTunes. Somehow it was synced to the phone and I can't find the tone on iTunes anymore.I tried everything I can think of to no avail... Can someone help me? It's driving me crazy.

I'm running iTunes 12.7 32-bit on Windows 10, and my phone is iPhone 5s ios 11.1...