It appears you are referring to a Jain Tirthankara, most likely Lord Munisuvrata Swami, the 20th Tirthankara in Jainism.

The main annual festival (Janma Kalyanak or birth anniversary) of Lord Munisuvrata Swami is celebrated on the Chaitra Shukla Ashtami (the 8th day of the bright half of the month of Chaitra) according to the Jain lunar calendar. This usually falls in March or April in the Gregorian calendar, but the exact date changes each year.

If you are asking about the weekly day associated with Lord Munisuvrata, in Jain tradition, Saturday (Shaniwar) is considered especially auspicious for the worship of Lord Munisuvrata Swami, and many devotees observe special rituals or fasts on this day in his honor.

If you need the specific date for this year, please specify the year or check a Jain calendar for "Munisuvrata Swami Janma Kalyanak."