Apple How do I transfer a ringtone to an iPhone 6s?

The steps change from time to time but this is a recent enough tutorial that maybe it still works: https://www.howtogeek.com/248489/how-to-add-custom-ringtones-to-your-iphone/
Good luck!

 

iTunes is an one-way tool and has copyright protection, so that it has no ability to export ringtones from the device to the computer directly. That's why you need an iPhone Ringtone Transfer program to act the best assistant here. With the MobiKin Assistant for iOS, you can transfer or copy ringtones from iPhone 6S to PC selectively or in a batch. In addition to the ringtones, other files like music, movie, photos, playlist, etc. can also be transferred to your personal computer with the help of iPhone Ringtone Transfer program.

 

Here is the guide to solve your problem check the given link