Allah is already ready to forgive us believers. We just need to repent and ask Allah’s forgiveness. With istighfar we seek Allah’s forgiveness. Saying “Astaghfirullah” (I seek forgiveness of Allah) is known as Istighfar.
Some istighfar dua are as follows:
“O Allah, You are my lord, No one is worth to worship except you. You created me and I am your slave, I repent for I have transgressed against my self by committing sins, You are most merciful and forgiving please forgive me. I seek refuge in you from the evil I have done. I acknowledge all the blessings you have bestowed upon me. No one can forgive my sins except you so please show mercy on me and forgive me.”
“O Allah, You are most merciful and forgiving. You love to forgive so please forgive my sins that I have committed knowingly and unknowingly . I worship to you and none. I am not perfect but I am at-least a Muslim. You are my only hope. No one can forgive me except you. Ya Allah forgive me and stop me from committing further sins, show me right path.”
“Ya Allah, You are one and only one, I do not associate any one with you. You are my lord. You are most merciful and forgiving, You love to forgive so please forgive my sins.”
“Ya Allah, You are most merciful and forgiving so please forgive my all minor and major sins and guide me to straight path.”
