Method 1: Add Ringtones to iPhone via iTunes.
Steps: 1. Plug your iPhone into the computer with the USB cable. iTunes will launch automatically. If not, double-click the icon of iTunes to start it.
2. Click “File” on the upper left corner of iTunes, and then click “Add File to Library”. Select ringtones from computer. Or directly drag ringtones to your iTunes library. You can also click on Tones from your iTunes library and drop the ringtones there.
3. After the ringtones being synced to the library of iTunes, click Tones Library under the Settings and choose to sync all tones or selected tones. Then click Sync button to sync ringtones to iPhone.
Method 2: Add Ringtones to iPhone via third party program.
Steps: 1.Run Leawo iTransfer and connect iPhone. The software will automatically detect the libraries of the iPhone, and then display the libraries in the left sidebar.
2.Choose Ringtones library and then the contents will be displayed in the right part. If no ringtones are available in your iPhone, you will see an “Add Files” button in the window, and you are allowed to select files from computer. If you have existed ringtones in iPhone, you will need to click “File > Add > Add Files/Add Folder” at the upper right corner to select ringtones from iPhone. Or click “Add” button at the upper left corner; or right-click “Ringtones” library to add ringtones from computer.
3.After selecting ringtones, Leawo iTransfer will begin to transfer ringtones to iPhone. The progress bar will notice the percentage of the transfer process. When the transfer is finished, you will get the ringtones in your iPhone.
Here is the tutorial you can refer to: https://www.leawo.org/tutorial/how-to-add-ringtones-to-iphone-6.html?qa=1409