Every report goes straight to the developer, and every one gets read.
A structured form: pick what kind of feedback it is and which part of the app it's about, write what happened (or what your idea is), and for bugs, optionally attach a diagnostic log to make it far easier to track down.

Diagnostic logs contain workout activity, timestamps, and error details — never your password or sign-in tokens — and they make bugs far easier to find and fix, so leaving the switch on is the fastest way to get a fix. Reports are limited to 10 per hour per account, which only matters if you're sending a flood of them at once.
Related: "About & support".