The CSV file provides the description of the traffic that the performance AXI Traffic generator must generate. One default CSV is packaged as a part of the IP. After creating a functional block design and generating output products, you can locate the default CSV file in the following directory
./<project_name>.ip_user_files/mem_init_files/default_aximm_synth_tg.csv.
You can copy this file to a custom location and modify it according to the type of traffic you want to generate. As a user, you can now use the custom CSV. Specify the custom CSV's path in the Path to user defined pattern file (CSV) option of the Synthesizable TG option tab in the GUI.
See AXI4 Traffic Pattern CSV Format for more information on CSV command format.