Should I donate the value of the computer I received as an award for being among the city's top students, knowing that I obtained it through cheating on exams, and years have passed since then, and I don't know if all students cheated or not, especially since my ranking was tied with another female student?

If you cheated on exams and received an award, this award is not lawful for you, and it must be returned to the granting entity or its equivalent value must be repaid, because it was granted based on you being genuinely among the top performers, not through cheating. You are not obligated to inform the entity; it is sufficient to deposit the value into their account or pay it to them as a donation. If returning it is not possible, then donate its value to the purposes of the entity, such as purchasing a computer for a school affiliated with them. This award is not lawful for you, even if others cheated. You must repent from cheating because it is one of the major sins, as the Prophet, peace and blessings be upon him, said: "He who cheats is not one of us."