We do not have a direct scripture that explains how to ask for forgiveness. We do know that we must come to the Father through Jesus. We also have a guide in the prayer of Salvation of confessing with the mouth and believing with the heart. We believe that God would want the same level of heart-sincerity. We also know from scripture that God asks us to forgive those who have wronged us.
Use this as a guide, as long as you: come to the Father through Jesus, confess with your mouth, believe in your heart, forgive others.
Guided prayers:
"Father, I come to you in the name of Jesus. Father I have held unforgiveness to someone who hurt me and I am forgiving that person now. Father I have also wronged others and knowingly committed sins, I ask you Father God to forgive me. Father I believe you hear me and you forgive me. I receive your forgiveness. Thank you for forgiving me Father. Thank you for interceding for me Lord Jesus. Thank you Holy Spirit for convicting my heart.