The unconscious mind is a difficult aspect of human psychology and it is the quality of our unconscious mind, unaccessible as it is to us, that has prompted this question. There indeed are aspects of the self that some people do not remember, especially if there has been trauma.
We can repress the memory. Repression is like shutting off the light so that you no longer can read a journal entry, forgetting its contents. Repression is a form of psychological defense against anxiety and is not necessarily a bad thing in the short-run if we need to re-group in order to move ahead in life. Yet, if there is unresolved trauma and we do not deal with it, this can be like the pebble in the shoe—a constant low-grade annoyance that will not let us rest. Sometimes it can cause great distress and we have no clue why we are feeling distress.
My best advice on this fascinating question is this: Deal directly with the deep hurts that are accessible to you. Forgive as best you can. Then be vigilant in asking the question, when you are ready, ???But what else is in my past that has hurt me???? As you gain both strength through forgiving and proficiency in the forgiveness process, this can engender in you a confidence that you will not be overcome by traumatic injustices. This further aids you in lowering—slowly and across time—the psychological defenses such as a rigid repression that block the memory.
As a person, for example, forgives her father for Injustice A, B, and C, eventually she may be ready to tackle the issue of sexual abuse. Having confronted injustice that may have surrounded the sexual abuse and having grown in confidence that she will not be crushed by her own anger, that which is unconscious may become subconscious (just below the level of consciousness). It is here that fleeting aspects of that repressed memory may enter into consciousness, allowing the person to finally confront the abuse.
One more point involves false memory. It can happen that a person thinks he or she was abused and this is not the case. This, then, becomes a horrendous injustice against the accused. The false memory is centered on unhealthy anger, now displaced inappropriately onto someone who does not deserve it. The practice of forgiveness for genuine injustices against those who truly have been unjust to us can reduce unhealthy anger, making the displacement of anger into a false memory less likely.