How to add your own ringtone to Android
If you find your ringtones other places — or have one you just need to add to the phone — then you'll need to get it into the proper folder in the Android file system, and that requires a file manager app. Now, some phones have file managers on them out of the box, but if not, you'll need to download one from the Google Play Store, like Solid Explorer. Once you've installed a file manager and downloaded the ringtone you want to your device, we need to move it to the proper folder:
Find and long-press your desired ringtone in the Downloads folder. After long-pressing the first ringtone, you can tap more ringtones if you wish to copy multiple sounds at once.
Tap Copy. The icon may vary from file explorer to file explorer, but on Solid Explorer, it's the icon with two documents stacked on top of each other.
Swipe in the menu from the left side of the screen.
Tap Internal Memory.
Tap the Ringtones folder. If you want to set the sound you're moving as a text tone or an alarm, you would tap the Notifications folder or Alarms folder.
Some phones' Settings app will see the new ringtones immediately, but just in case yours doesn't go ahead and reboot the phone. Upon reboot, the new ringtones will appear in the list of available ringtones. Now all that's left to do is set the ringtone.