Depending on the device (or devices) you are using, I have found two simple ways to record your voice along with the accompaniment
1: Play the accompaniment on a secondary device, use voice memo or similar app to record, then share file through that app
2: Use the screen capture feature on your phone. Make sure the mic is enabled by long-pressing the screen-cap icon, use headphones, share normally
Please let me know if neither of these options are available to you we will find an alternative.