What you need is one of these, assuming your TV has a coax input. Just plug the Atari cord into this and screw the other end into the TV

Atari 2600 RF TV Coaxial F Plug Female Adapter https://www.amazon.com/dp/B0028MXOF6/ref=cm_sw_r_cp_apa_i_XBimEb5S6DFQ3