That is a 'big' question. I first thought of school memories and people looking over the shoulder of the person in front of them or at the desk next to them. I did not think of a relationship until reading other answers. That said 'cheating' itself IMHO is universal excluding no one. As suggested the context for the cheating would need to be known as well as the offense itself.
Regarding forgiveness a whole new subject is entered upon. Forgiveness has been written on extensively in many venues and genre. There are philosophical, religious, and day-to-day practical. Forgiveness is unique as it IMHO is 'power' rather than power exercised. In other words the effect of forgiveness is not the same as forgiveness. Forgiveness is autonomous while having property of being universal. IMHO forgiveness seems to have the property of the Law of Reciprocity. Exercised it effects both the forgiver and the one forgiven.
An analogy may be forgiveness is like the horsepower of an engine. It is there all 600 HP. It is idling at a standstill having both available energy and potential energy. At task is application when the engine is under some kind of load. Then giving it the gas to overcome the load. That is forgiveness exercised, however the power is the same . . . 600 HP. Discovered is there is power, an action, and then an effect.
All of that does not answer 'How'. How to forgive of itself is at task. Then comes the context of the offense. Finally the 'who'. Or, asking questions for exercising forgiveness remembering of itself is a power would be necessary. One firstly has to have an understanding of forgiveness acceptable for oneself. Then comes the offense. If one cannot forgive the offense no matter the 'who' then of course 'who' does not matter. 'Who' most likely is a variable with emphasis on relationship and/or the relationship.
A note is forgiveness can be exercised while responsibility remains for the offense. Those are two different matters. An example is how many times on TV has one seen a person in a courtroom usually a relative stand up saying they forgive the criminal. Yet, the criminal still goes to jail, which is an action of responsibility. Or, one forgives the student who cheated, yet that student's test is given a zero on it. There is still responsibility for the offense.