Hi!
To create front-end filters check chapter 8 from the documentation: https://goo.gl/ZlvD0v
Additionally, there is a Video Tutorial available for creating custom field filters: https://goo.gl/obe1r5
Refunds are handled by Envato, but unfortunately they have no-refund policy with very few exceptions. You still have the product with lifetime updates avaliable, so you can may use it on a different project.