I swore by Allah not to cheat students, but I broke my oath. What should I do?

You must repent to Allah for cheating students in exams, because it is a betrayal not permissible শর‘ঈ (religiously), and you must not return to this act. You also owe expiation for your broken oath, by feeding ten needy persons, or clothing them, or freeing a slave. If you are unable, then fast for three consecutive days.