This app allows you to pick mp3 files, send them to the Gear app and set as Custom Ringtone. Instruction is provided inside the app. Launch this app first and use it to launch the gear app.
It's safe to download this application. Claybikeltd is the developer of the app that can be found in the Tools category. Custom Ringtone was downloaded and set up by over 50K users and its most recent stable release was on Dec 6, 2017.
Google Play shows that this application is rated 2.8 by its users. Download the free installation package of Custom Ringtone 1.5 and take a look at users' reviews on Droid Informer. The app can be launched on Android devices 4.4 and above.