Most of the lies Christian Nationalists believe originated with religious leaders who interpreted the bible literally instead of symbolically. Therefore, the only way for them to stop believing lies is if they are exposed to the truth.
Telling the truth about the bible will be hard for people who are not themselves convinced of the truth. It would be good, therefore, for people who want to tell the truth to Christian Nationalists to first be convinced about the truth in their own hearts and minds before they attempt to share the truth with others.
A good place to begin is to study the following links: