When pasta is ready, drain the water. If the sauce is thick enough for you, then you don't need to do anything else. Pour the sauce on the pasta and enjoy!
If you prefer a thick and gooey sauce, then heat a frying pan on low/medium heat. Add pasta and the mac and cheese sauce and 1 Tbsp tapioca starch and mix thoroughly. Stir continuously and heat the sauce until bubbling. After 2-3 minutes, it thickens. Enjoy!