Anything exported from a context="module" script block becomes an export from the module itself. If we export a stopAll function from AudioPlayer.svelte...

<script context="module">
  const elements = new Set();

  export function stopAll() {
    elements.forEach(element => {
      element.pause();
    });
  }
</script>

...we can then import it in App.svelte...

<script>
  import AudioPlayer, { stopAll } from './AudioPlayer.svelte';
</script>

...and use it in an event handler:

<button on:click={stopAll}>
  stop all audio
</button>

You can't have a default export, because the component is the default export.