Source: http://docs.csiamerica.com/help-files/etabs/Menus/Define/Section_Properties/Frame_Sections/Frame_Section_Property_Reinforcement_Data_Form.htm
The above might work for you. I don't have SAP2000 installed so I can't really check what I find on internet but I do remember that you could either design a new beam or check existing one very easily. If the above doesn't work, try this link:
https://www.researchgate.net/post/How_to_provide_beam_reinforcement_in_sap2000_with_R_F_to_be_check_option_just_like_option_provided_for_column_in_sap2000
Things have changed so much since I was working on SAP200.