On Call Details page of your call, in the bottom Files section, click on the Wide Source video of the person you’d like to generate VFX for:
Right-click on the timeline at the timestamp where you’d like the VFX clip to start
Choose your custom VFX settings. Click Export.
You will receive an email when your export is complete, or you can check back in ~10 mins.
The video will show up as a “VFX Clip” in the Exports section of your Call Details page.