We follow because adeshwar bhagwan did it but on what belief Bhagwan adeshwar dada did navanu jatra

Navanu Jatra (Navanu Yatra) is a revered Jain practice linked with Adeshwar Dada (Adinath), the first Tirthankar. It is not a scriptural command, but a traditional penance strongly followed by many Jains at Shatrunjaya Palitana.

Belief and purpose (arth) in short:

• The yatras are done to seek forgiveness, purify the soul, and advance spiritual progress (prayaschit and tapas) before the Almighty Adeshwar Dada and other Tirthankaras.
• It involves climbing Shatrunjaya Hill many times (traditionally 99 rounds) with strict vows and self-discipline, including a careful code of conduct (such as modesty, non-violence, and often fasting during parts of the yatra).
• It is a powerful personal devotional act believed to help lessen karmic burden and move the devotee closer to liberation.

Notes:

• Different Jain traditions (Digambar, Shwetambar) may emphasize slightly different customs or timings, but the core idea—Navanu as a strenuous, disciplined penance in honor of Adeshwar Dada—remains common.

You can read more here