Your honest prayer is heard by God and I am thankful you shared it so openly. You are right about one important thing. You cannot do this on your own, and admitting that is actually the place where God can begin to work.
Many people have been taught that if they smoke they cannot be a Christian or cannot come to God until they first quit. That teaching puts the cart before the horse and leaves people in bondage. They want to be close to God but feel they must break the habit first, and when they fail they feel even further away. The truth of Scripture is that salvation comes through faith in Jesus Christ alone. You do not have to clean yourself up to be accepted by Him. You come to Him as you are, you receive His forgiveness and new life, and then He gives you power to see change in areas where you have felt helpless. Quitting smoking is a good and wise desire for the health of your body which God has given you, but it is not the condition for His love or for being His child.
Habits like this can feel automatic. Before you even think, the craving comes and the response follows. In that way it is like other appetites of the body or like a quick temper that flares before you can stop it. God created your body and He keeps the vital functions going without your thought, but He has left other choices under your will, and those are the very areas where we can get into trouble. God never intended for those appetites to rule you. His intention is that when you are born again by His Spirit, the Spirit would be in control and the cravings of the body would be brought under His rule.
That is why self help formulas so often fail. The apostle Paul described this struggle in Romans chapter 7. He tried to change by his own effort and found he could not. At the end he stopped asking how can I do better and cried out who shall deliver me. The answer is outside of ourselves. The path Jesus spoke of is the path of self denial and the cross. It means coming to the end of self rule, reckoning that your old nature was crucified with Christ, and then following Him and asking Him to lead and empower you day by day. Victory is not you trying harder in your own strength. It is Christ living in you and His Spirit giving you strength to say no when the craving says yes.
God knows the power of these cravings and He is not surprised or disappointed by your struggle. He loves you and He is patient. He wants to help you and He is in control even in this situation, working for your good as you trust Him.
Bring each craving to Him in the moment. When it comes, pray simply and honestly, Lord help me, I need Your strength right now. Let His Word fill your mind. Seek fellowship with others who will encourage you and pray with you, and do not be afraid to get wise practical help for your body as well. Each time you turn to Him instead of to the cigarette, you are learning to let the Spirit rule rather than the appetite. Over time, as you walk with Jesus, you will find He is giving you victory in an area where you once felt you had no control.
I am praying for you.
Father, I bring this dear one before You in the name of Jesus. Thank You that You love them and hear their prayer. Thank You that salvation is by Your grace through faith in Christ and not by our ability to overcome habits. I ask that You fill them with Your Holy Spirit and give them Your power to overcome these cravings. In the moment of temptation, be their strength and their deliverance. Bring peace instead of anxiety, and help them to know they are Yours and that You are with them. Restore health and give growing freedom, that their body may be strengthened to serve You. Keep them close to Jesus and let them experience the life and victory that comes from Him alone. Amen.