We all have done bad karma,so if something is bugging my mind constantly
(Like killing some mosquito)
what is the solution for me,what can i do to overcome it/or to forget it?
Short answer is, you should not forget bad choices. You should learn from bad choices.
Kukucca is characterized by regret. It's function is to grieve about what has or what has not been done. It manifests as remorse. It should be regarded as slavery.
--from Visuddhimagga XIV, 174
The Dalai Lama was working with an American psychiatrist who was interviewing him for a book on happiness. The subject of remorse was broached: His Holiness explained that one time an elderly Buddhist man came to see him to ask for instructions on how to do a very difficult Yoga pose. The Dalai Lama told the man that he was too old and should not attempt the pose as it would be too dangerous. The old man thanked the Dalai Lama, went home and killed himself so he could be reincarnated as a younger, healthier man who could attempt the pose. After hearing the news, the Dalai lama was overcome with guilt at being the reason for another man’s death.
“So how did you deal with that?” asked the interviewer. “How did you get rid of the remorse.”
The Dalai Lama sat there in silence for a minute or two, thinking hard about the question.
“I didn’t get rid of it” the Dalai Lama explained. “It’s still with me every day. I just continue to live with my heart open.”
So, what does it mean, "to live with one's heart open"? It means to see it like so: "What was done in the past cannot be changed. Thinking about it will not help me undo it. Now I have learned my lesson and will not make exactly the same mistake. I don't know what will happen in the future, but if similar situation comes up, or even a completely different situation -- I will do my best!"
Forgetting our past karma is not skillful, but if the memory of a past deed is amplified to the point of being unhealthy, you may want to write down the deed on a piece of paper. For example, you can write, "I took a parking spot from an old lady three years ago today." Then leave the paper on a coffee table or desk for a couple of days where you will see it several times in your day. This way, you may be able to see the deed in a neutral context. Originally, my sister suggested this method for getting rid of a song that repeated in my mind.
The best way to overcome this is to work with the object and learn about it.
In Buddhism we overcome "problems" by learning about them and thereby understanding them.
Remorse is one of the 5 hindrances. They are objects that can slow one down on the path. They block progress in e.g. meditation.
When a hindrance is present, make a mental note that a hindrance is present. Keep observing the hindrance with mindfulness, in the present moment and note it as "remorse, remorse", until it ceases.
This way you can use the hindrance to cultivate insights, i.e. the 3 signs of existence.
The best way is to accept them. Accept them and let them go. Don't force them to go away, know them and they will go home on their own accord.
And you are not really forgetting anything, you are just accepting things that arise. Because they arise in the moment, they belong to the moment.
I wholeheartedly recommend reading "The Teachings of Ajahn Chah" as you will find great Dhamma talks there.