How to update geometry using External Visualizer?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](https://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](https://www.open3d.org/docs/release/) and the [latest documentation](https://www.open3d.org/docs/latest/) (for `main` branch).

### My Question

I am using open3d's External Visualizer to visualize point clouds in a remote pc (unfortunately, X forwarding is not allowed). Currently, I have a script in the remote server that draws the point cloud: `draw = o3d.visualization.ExternalVisualizer(timeout=timeout).draw` and `draw(pcl)`, and on my pc I run `python3 -m open3d.visualization --external-vis`. However, when I want to view another pointcloud, I have to close the current visualization in my pc and restart it (`python3 -m open3d.visualization --external-vis`) which is cumbersome when repeating (I am using it to view progress in my training).

I was wondering if there was a better way to do it, perhaps something similar to update_geometry: `o3d.visualization.Visualizer.update_geometry()` or some way to clear geometries within the renderer gui?

I would be happy to provide more information if that's necessary. Here is some basic info: open3d version in both remote server and local system is `0.18.0`.