Child.svelte

<script>
  // since Child is wrapped inside VideoCallFunctionProvider,
  // we can access the context value here
  import { get } from '.VideoCallFunctionProvider.svelte';
  
  const { triggerVideoCall } = get()
</script>

<button on:click={() => triggerVideoCall()}>
  Call John Doe
</button>

Dashboard.svelte

<script>
  import VideoCallFunctionProvider from '.VideoCallFunctionProvider.svelte';
  import Child from 'Child.svelte'
</script>

<VideoCallFunctionProvider>
  <!-- you'd wrap all dashboard stuff here -->
  <Child />
</VideoCallFunctionProvider>

VideoCallFunctionProvider.svelte

<script context="module">
  export const KEY = 'video-call-func-ctx';
  export const get = getContext(KEY);
</script>

<script>
  import { setContext, getContext } from 'svelte';
  
  function triggerVideoCall() {
    // ... logic here
  }
  
  setContext(KEY, { triggerVideoCall });
</script>

<!-- You may put the video call markup here -->
<slot />