First, forget what time it is for an hour. Do it regularly every day. Then forget what day of the week it is, and do this regularly in company for a week. Then forget what country you are in, and practice doing it in company for a week, and then do them together for a week with as few breaks as possible. Follow these by forgetting how to add or to subtract. It makes no difference. You can change them around after a week. Both will later help you to forget how to count.
Forget how to count, starting with your own age, starting with how to count backwards, starting with even numbers, with roman numerals, starting with fractions, with the old calendar, going on to the alphabet, forgetting it all until everything is continuous and whole again.