They replied, “Believe in the Lord Jesus, and you will be saved—you and your household.” – Acts 16:3

A 2016 article in the Washington Post was written by Matt Rota about Dr. Richard Gallagher, called “As a psychiatrist, I diagnose mental illness. Also, I help spot demonic possession. How a scientist learned to work with exorcists”.
I’ve been reading Dr. Gallagher’s book so skimmed the article. It’s pretty interesting.
He described his meeting a self-described witch through a Catholic priest who knew of Dr. Gallagher’s background and brought the woman in to rule out whether she had a mental illness. Dr. Gallagher described this witch as presenting with paranormal abilities due to being demonically possessed, and that she could not be diagnosed as being psychotic.
A YouTube video from 2020 documents an interview with Dr. Gallagher on Inside Edition.
At the time of the article’s being published, demand for exorcisms keeps rising. In Indianapolis, Rev. Vincent Lampert received about 20 inquiries per week for exorcisms in 2016 but the demands have increased to over 2,000 requests per year, or roughly 28 requests per week in 2021.
There is much to know about people who are probably demonically possessed or demonically oppressed and what happens to them.
Whether they give their lives over to the demons who are harming them, whether they die demonically possessed, or whether an informed Christian who has been trained to understand the strange symptoms of the demonically assailed has the predisposition to hang tight and learn how to invade the lives of these victims through prayer and belief, calling upon the Lord Jesus Christ to help them guide a person who wants to be saved by Jesus needs understanding, and support to be free of it.
A victim must ask for help and want to give their lives to Jesus, instead of still interacting with spiritual presences. These people should be asked to talk about their experiences if they want to, but more importantly, be engaged by Christians into prayer for their guidance.
Victims need to want to come out of a demonic presence. Knowing how might best be handled by trained spiritual advisors of the Christian faith.
I found a webpage here with information about demons, exorcisms and spirits. It is a suggestion only. I am unaware of who wrote the pages of this website, but the initial reading I did seemed appropriate and seems to contain some common sense information.
A website I’ve used regularly provides an answer to the question, Can a Christian be demon possessed? Short answer is no. But spiritual warfare against Christians does exist.
If you are having problems with demonic possession or oppression you must ask yourself whether you are wanting to be free of it. If you go back and keep trying to summon up demonic activity you will never be free.
The only way to free yourself of demonic possession is to turn to the Lord Jesus Christ and pray often throughout your days to see any progress. Jesus answers prayers. It may take some time depending on your walk with the Lord. I do not know and cannot speak for the Lord but I would seek help from a Christian church. Don’t go it alone without help. Get a support system around you. Let someone at a church you trust and find out about get you a referral to a knowledgable pastor who can guide you and help you along the way.
You must start a daily walk with God, the Lord Jesus Christ. There is no other way.