Perhaps you have heard about a prayer called "the sinners prayer" or you may have even recited one. However, I don't think a recited prayer should replace a heart and mind that is truly thankful to God for His salvation from the deserved punishment for breaking His laws.
Rather, I would suggest that if you desire to pray, talk to Him as you would talk with a friend. Thank God for sending Jesus and taking the punishment of sin for you. Thank Him for His unmerited forgiveness. Cry out to Him with your whole heart.
My prayer for you is nothing more than for your salvation from the wrath to come. (God's judgment against sinners)
Where you and I spend eternity is a matter of life or death.
"Godly sorrow produces repentance leading to salvation..." 2 Corinthians 7:10a
If you talk with God and trust Him for His forgiveness of your sin, you might not see flashes of light or hear a great chorus of angels playing pretty “hallelujah” music. But you will be given a new life. (This new life is sometimes referred to as being born again or rebirth).
As a born again Christian you will be given new desires and seek to please God. And if you have put your trust in Jesus, please don't hesitate to tell others who have also professed faith in Jesus Christ as their Lord and Savior. Who is Jesus?
Then you'll want to get yourself a Bible and with God's help, obey and read it everyday.