In Jainism, there is no fixed “birth year” in the Gregorian/BC–AD sense for Bhagwan Rishabhanatha (Adinath).

Traditional Jain view:

• Rishabhanatha is the 1st Tirthankara of the present avasarpiṇī (current descending half of the cosmic time cycle).
• His birth is placed in an extremely ancient era, measured in sāgaropama / pūrva type units of Jain time, not in human historical years.
• Because of this, Jain scriptures do not give a date like “XXXX BCE” for his birth.
• Modern scholars sometimes try to estimate historical periods, but these are their theories, not accepted traditional Jain dates.

So, from a pure Jain dharma standpoint:

• We say: Bhagwan Rishabhdev took birth in the very ancient past of the present avasarpiṇī-kāl,
• and we do not convert that into a specific calendar year.

If you want to read a simple explanation in Jain terms, you can see this JainKnowledge answer on his birth period and life story here: