Add Google AdWords Conversion Tag to "Thank You" page

Hi.. I need to add a Google AdWords conversion tracker on my "Thank You" page that appears after web visitor purchases my product. Problems: 1) I can't really find that "Thank You" page 2) I tried using Google Tag Manager to add the conversion tag, Google Tag Manager placed the tags to all of my web pages. So can you add the Conversion Tag to my "Thank You" page only? IMPORTANT: We can only work via Team Viewer only. Thank you.