Ratnatraya means the three jewels of Jain path: Samyak Darshan (right faith), Samyak Jnana (right knowledge), and Samyak Charitra (right conduct).
There are no fixed “dates” for Ratnatraya itself in any month. Ratnatraya is a timeless framework for spiritual progress, not a date-specific event.
If you meant a festival or period in Bhadrapad (the month around August–September in many Indian calendars), the major Jain observances that fall around that time can vary by tradition and year (for example, Paryushan in the Shwetambar tradition, which shifts each year). Digambar timings can differ as well. Dates are not intrinsic to Ratnatraya but to those festive observances.
If you share a specific year and whether you follow Digambar or Shwetambar practice, I can give exact festival dates that fall in Bhadrapad for that year.