PAS is horrible. The worst it inflicted on the child. Yet I have seen hope. The stronger your relation the higher the probability. We often get second and third and more chances.
There is no one size fits all solution but there are things to do. Don't give up hope. Never listen to people who tell you to dump your child. Never be angry at your child. Yeah easier said than done! Yet it is absolutely required. Remember nobody is perfect. PA relies on our own mistakes. It might be as simple as failing to act to prevent it. Or may be that we don't reform our faults. We all have buttons and they can be pressed. We need to recognize our children's needs. When that happens we open the door to PA. We can close it if we recognize it. Yet we fail too often. When it happens we get angry. PA relies on magnifying our flaws. They press our buttons and we react. Don't react. Our children naturally love us. They don't want to hate us. If PA happens to a young child the law may help. When the child is older law and force are ineffective. You can not legistlate love. You need to prove it. Reach out to your child. It may be impossible if the child is isolated. Never give up. Keep at it and sooner or later the message will get through. The best is when your child reaches out to you. When they do return unconditional love.

Your child is like a drowning person. When you are so lucky they reach out to you then take their hand. I told people that I am going to take my child's hand. We swim or sink together.

Your child has more instinct than you may know. They get it. They know who loves them. Never and I mean never disparage the other parent. Your own actions will do the job.