Okay, so as you are using html on your lightbox, you will need to first get the response back from the html to your lightbox first by using the html component.
How do I send data between my page and an HTML Component?
You can send and receive messages between your page and an HTML Component using the postMessage() and onMessage() functions.
https://support.wix.com/en/article/corvid-working-with-the-html-element
https://www.wix.com/corvid/reference/$w.HtmlComponent.html
https://www.wix.com/corvid/forum/corvid-tips-and-updates/example-fullscreen-with-htmlcomponent
Then you would have values to pass back to the page from the lightbox using the code.
How do I pass data between a page and a lightbox?
When you open a lightbox using the openLightbox() function, you can pass an object containing data to be used in the lightbox. In the lightbox’s code, you call the getContext() function to retrieve the data sent by the openLightbox() function.
When you close the lightbox using the close() function, you can pass an object containing data to be used by the page that opened the lightbox. This data is retrieved from the resolution of the Promise returned by the openLightbox() function.
https://www.wix.com/corvid/reference/wix-window.lightbox.html
You might just be easier to have the html component popup on screen when needed and not in the lightbox, so simply collapse it on load through the properties panel and expand it in code when needed, especially if you use the full screen version etc.