Nandavrat Gawali looks like a term I’m not certain about in Jain texts. If you meant Navpad Oli (Navpad Gawali), here is the Jain understanding:

• Navpad are the nine supreme posts in Jinshasan: Arihant, Siddha, Acharya, Upadhyaya, Sadhu/Sadhvi, Darshan, Gyan, Charitra, and Tap. Each day of the Navpad Oli is dedicated to one of these nine posts and their qualities. The practice emphasizes concentration on the path to liberation and to honor the leadership and example of these revered beings. ( jainknowledge.com)
• Navpad Oli (Ayambil Oli) is a two-times-a-year, nine-day festival. During it, many Jains perform Ayambil Tap: they eat only once a day and avoid tasty items like milk, ghee, oil, sugar, and fried foods, consuming simple boiled grains instead. This fast is meant to purify the mind and body and to strengthen spiritual discipline. ( yja.org, jaina.org)
• The significance is deep: it reinforces self-control, detachment from sensory pleasures, and devotion to the Jina’s teachings, with the aim of purifying karma and advancing on the path to liberation. The Navpad framework also reflects Digambar/Shvetambar traditions’ shared reverence for these nine essential facets of spiritual progress, though minor ritual details may vary by tradition. ( jainknowledge.com, yja.org)

You can read more about Navpad concepts and the Acharya Pad role here