You can ask for Informal Dispute Resolution (IDR) from the court. You must first try to get your employer to agree to a change in doctors. If this doesn't work, you or your employer can ask for help through the IDR process. A court staff member will try to help you and your employer agree. If that doesn't work, a motion or petition (lawsuit) can be filed with the court.
To learn more check out Nebraska Worker's Comp.