Adding loader in Wix multistage form

I have wix multistage form with 5 video uploads and am trying to show/hide a loader gif to let users know their uploads are completed or being processed. But I’m not sure which event to add code for loader and how to know each stage is completed. I need to add the loader in middle stage.

Thanks.

Here’s a simple example of an Upload Preloader . You can see from this how to wire in a preloader, and then you can apply to your use case.