Reuven did an aveira. It wasn't a big one, but any aveira is wrong. Reuven had laughed at a cripple struggling to cross the street. Afterwards he didn't think too much about it.
Eventually Reuven married. The years passed as he worked and raised his family. One day his young son fell off a slide and broke his foot. For weeks, the boy hobbled around in crutches. One day Reuven witnessed the neighborhood children laughing after his son clumsily banged into a parked car. Suddenly he remembered the handicapped man that he had laughed at many years ago. "How can I do teshuva for laughing at that unfortunate person so long ago?" He felt terrible for days. He consulted his rabbi for an answer to relieve his guilt.
"Jews particularly feel guilty," his Rabbi explained. "This is because a Jew intrinsically knows what is right and wrong in the eyes of the Creator. When a Jew behaves in a way that is not befitting a human being, he feels guilty. The good news is that just as your soul is given the sensitivity to feel remorse it is also given the knowledge to figure out a way to remedy the spiritual malady that first caused him to sin.
Reuven thanked his Rav for his insight. He decided what to do and made a personal kabbalah to be different. From that moment on, he felt the deep joy that comes with integrating the decision to be new and improved.
The Kli Yakar explains that the p’sukim in the 6th aliya are referring to teshuva. A person can never claim he was not aware of the existence of teshuva. This is because Yisroel and teshuva were created before the world. (Pesachim 54a). Furthermore, a Jew needs no prompting to do teshuva. A Jew is automatically sorry when he does something wrong (which explains the standard jokes about JEWISH GUILT).
The Kli Yakar delves deeper. He points out that if a person "does an aveira in a certain place across the ocean with a certain woman" that this person may imagine that the only way to do teshuva is "to travel a great distance back to the place where the original aveira was done, find the original woman and resist doing the aveira". In that case most people will very likely be held back from doing teshuva because it is close to impossible to make such a journey and recreate such a situation.
Thus, the Kli Yakar explains that when the Torah says, "It is close to our mouth…" it is referring to vidui (heartfelt confession). And when the Torah says, "It is close to our hearts…" it is referring to charata (profound regret)
Any place you go, you take yourself with you. The desire to sin resides inside a person's heart and that is the location for teshuva as well. This is what is meant by, "It is not overseas or in some far-off place". Returning to the actual city is only a figure of speech. It doesn't mean we have to return to the scene of the crime. But what is essential for teshuva is a sincere motivation to live as a tzelem Elokim.