Existing members can navigate to their LifterLMS account page (defaults to the “My Courses” page and click the “Redeem Voucher” link at the top of screen.
We don’t really have a way to remove the sign up button as an option. What you’re attempting to do is outside the scope of what LifterLMS can do natively so you’d need to investigate our developer documentation and look through the codebase to try to find a way around the core functionality.
I think the fastest way to implement a workaround would be to create a custom membership purchase-link template and use a theme override to use your custom template rather than the default LifterLMS included template.
Take a look at the template at “templates/membership/purchase-link.php”
You can learn how to override default templates in your theme or child theme at https://lifterlms.readme.io/docs/template-overview#overwriting-templates-in-a-theme
Hopefully that gets you started and let me know if I can help any further,
