Hi – great question.
In that case you’ll probably be interested in overriding and customizing the wootickets/tickets.php template – you can find out more about this process by reading through our Themer’s Guide – but essentially you would copy the template of that name from the WooCommerce Tickets plugin directory and place the copy in your theme at a path something like this:
your-theme/tribe-events/wootickets/tickets.php
Adding your custom code to the top would probably work. I don’t know what shape that’s going to take, exactly, but essentially I imagine it would be a test to see if they don’t have a subscription – and code to display a link to the relevant page if so.
For assistance determining what that code should be you’d need to reach out to the Woo team as unfortunately we can’t guide you through customizations relating to third party plugins.
I do hope that gives you an outline of what changes would be needed in relation to WooCommerce Tickets, though, and of course let me know if you have any further questions 🙂