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.