We understand that you're struggling with intrusive thoughts about your former manager, and it's causing you distress. First, let's address the spiritual aspect of this situation. It's important to remember that our battle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms (Ephesians 6:12, WEB).
In this case, we need to pray for a spiritual disconnection. God has not given us a spirit of fear, but of power, love, and self-control (2 Timothy 1:7, WEB). You can take authority in Jesus' name.
Let's pray together:
"Father, please let your beloved, Anonymous, have no spiritual connection to their former manager. In Jesus' name, we bind any spirit of obsession or control that may be influencing this situation. Remove this former manager in Jesus' name to spiritually disconnect Anonymous from him, and remove him from their mind. May anything that has been spoken over Anonymous be broken in Jesus' name if it does not come to pass according to your Word and will, Lord. Please guide them, and help them to focus on what is true, noble, right, pure, lovely, and admirable (Philippians 4:8, WEB). Help Anonymous understand that they now have the mind of Christ (1 Corinthians 2:16). And this situation will be used for good (Romans 8:28), in Jesus mighty name we pray. Let your will be done. Amen."
Be careful when allowing someone to have influence over your thoughts and life. We have to resist the devil. (James 4:7). Now, let this be your prayer. Every time he comes to your mind, pray it out loud if you can and mean it with your heart:
"I resist you, (insert former manager's name), in Jesus' name. I will no longer have anything spiritual to do with you in Jesus' name. Amen"
In this battle, God assures us of victory. Remain steadfast in faith, and trust that God is working everything out for your good. If this person is harassing you physically also, please take steps to prevent this. God has provided persons in authority to help us. (Romans 13:1)
Lastly, although not mentioned, it is only through the name of Jesus that salvation can be obtained. You must call upon His name and confess with your mouth the Lord Jesus Christ, and believe in your heart that God raised Him from the dead to be saved. (Romans 10:9-10)