Find the nakshatra (and pada) the Moon occupied at any date, time and place. With a birth moment, this is the birth star.
Enter a date, a time and a city. The Moon crosses one of the 27 nakshatras in about a day, so the birth star rarely changes with a small time error, but the pada can.
Mon, 14 Feb 1994 · 09:42 AM · Varanasi
Do I need an exact birth time?
The Moon spends about a day in each nakshatra, so a small error rarely changes the star. A pada lasts about six hours, so it can shift; enter the time from the birth record where possible.
Which ayanamsa do you use?
Lahiri (Chitrapaksha), the standard used by most Indian almanacs, so results can be checked side by side.
Does the birth place matter?
Through the time zone: the same clock time in two zones is two different moments. Cities that share a time zone give the same star for the same clock time.