What should I do to get my son if his mother gave our son to her brother and moved?

Who has custody? Is that what you mean by parenting plan?

No body has legal custody, she just gave the child to her brother, with a written letter, and they moved to Hawaii, she is an addict and could not take proper care… and now Im out of prison and want my son.

Speak to a lawyer. If there is no official document giving her brother legal custody of your son, technically she would still have legal custody at this time, but he is acting as the custodial guardian. If your parental rights were never severed, you should still be able to have so say over what is going on, but if she had your parental rights severed while you were in prison, it will be much harder for you. You will most likely need a lawyer though since you don’t know the specifics of what her brother has at this time. You will need to find out who has legal custody and petition to get custody of your son.

Is there any way you can get in touch with her or her brother and tell him that you want you son back? You could try that first.

Just curious, but I thought you were a girl from your other questions and already had your child with you.

He/She is your child and if you have a birth cert. with your name listed, you can just go get him/her. Thats all you have to do.
If you have been removed legally, then that is a new problem requiring lawyers.