Format: M4R (Ringtone for iOS Apple Devices)
On your laptop (Mac OSX)
Using Finder (For macOS 10.15 Catalina and later):
Connect your iPhone to your MacBook using a USB cable.
Open Finder and locate your iPhone under "Locations" in the sidebar.
Click on your iPhone and navigate to the General tab.
Drag and drop the .m4r file into the General tab area. This will automatically transfer the ringtone to your iPhone.
Wait 10 seconds to sync the file to the phone.
Then, on your phone go to:
Settings
Sounds & Haptics
Ringtone