Dear mod, if I had understood how to install graphics card from this dumb manual, I would not be asking here.Page 12 in your case manual;
https://www.thermaltake.com/media/productattach/c/a/ca-1q2-00m1wn-00_core_p8_tg_manual_200422.pdf
shows you how to do so. If you zoom in and then count the screw holes, it's pretty evident where the brackets goes on the tray.