Any group exercise certification such as ACE, AFAA, ACSM (assuming you are in the US), would tell you how to safely plan a cardiovascular class. Line dancing, if done at a relatively constant intensity for a period of time, can be considered cardiovascular exercise. None of the certification texts will teach you line dances or line dance choreography (I have all 3 textbooks). You will have to learn your own dance moves. However, a group-ex cert would help you learn how to do a safe warm-up, what intensity and for how long you would do line dancing, how to cool down, and how to stretch.