Hi @RooRue,
you can fallow the flow like:
1. add a CTA(button or link) to show the webinar link.
2. Once the user click on the cta just redirect user to the form.
3. before submission, You just save some flag in browser in the form of cookie or local storage or session storage.
4. On submit redirect the user to the webinar page, in wbniar page if submit flag is not preset just show the message. if present then show the link.
this is just a straight forward implementation but can be changed based on your security requirements.
Hope this helps
Umesh Thakur