Sadly, there is no cure yet for this condition and the only thing that may help is to listen to something else that will help cancel out the ringing.
The app I like best is Brain Wave, 32 Advanced Binaural Programs by Banzai Labs. If I need to get to sleep I'd listen the sound of rain, which gives a very comforting feel that helps me sleep. If I'm reading or at work, I'd either listen to the forest or the sound of a running brook.
But these days with Apple Music, my favourite songs work too.
Anything is better than constant ringing that won't go away.