Navchandi yagna is a Nav Durga puja. This puja is to help make wishes come genuine as well as for health and fitness, prosperity, toughness. Also the prosperity, accomplishment and all kinds of other challenges during the life. In other scriptures, Chandi is portrayed as "aiding" Kali in her struggle https://a-z-directory.com/listings13053374/5-essential-elements-for-navchandi