Where to add code to pull through order details

Please let me preface this with the fact that I am not very tech savvy. I am unable to find the WP page section where I can paste [TRFW_ORDER_DETAILS]. I already have a thank you page set up and have successfully redirected completed orders there, but do not know where to add the aforementioned code so the order details can be generated. I am looking forward to your guidance on this matter.

The page I need help with: [log in to see the link]