My husband is in jail and is wanting to sign all his rights over to his son that is with another woman do to her not letting him have any rights to him. How would he go about doing so or what could I do to help?

You can not do anything really as you are not a party to it.
Since he is in jail there is not much he can do at this point. Of course he can not just sign over his rights, he does not have to use them, if he wants to see the child, he files in court for a order to visit, but he can not just sign over his rights.

Did you read this?

Bottom line: even if he could "sign over rights", that's not going to affect his responsibility to pay child support, unless and until the child is adopted.

And his responsibility to pay child support has absolutely no relationship to whether the mother allows him to see the child.

Well, if he is in jail, that could be why he can't see his son. But the courts view visitation and support as separate items. And they are treated separately by the courts.

As notied in the post AK linked to, he's not going be allowed to sign over his rights and is definitely not going to be allowed to stop his support obligation.