How to make my Landing page calculate the CVR based on how many people clicked a external link button and not the next step link?

Technical
1

So in Funnelish, we can see the CVR of a page based on how many people went to the next step. It can do that because the next page is inside the same funnel of funnelish.

But if there is no next step inside that funnel, instead an external landing page on Shopify.

So how can I make the CVR of this funnelish page based on how many people went to that external link or clicked the CTA?