In Varshitap, the day does not depend on the weekday like Monday or Tuesday. It is counted by the Jain lunar tithi and by the sequence of fasting/rest days in your sankalp.

If by “chatt” you mean “chhath” / the sixth day, then:

• Start counting from the day you began Varshitap.
• Follow the tithi-based Jain calendar.
• The exact day can change because Jain observances follow lunar dates, not only the English calendar.
• For exact determination, check the Jain Panchang or ask your guru/pravachan guide.

Simple rule:

• Count according to tithi
• Do not count only by weekdays
• Sunrise and tithi change are important

If you want, I can also explain the full Varshitap counting method in a simple day-by-day way.