How to find all planetary positions on starting of every Yuga?
Executive answer to planetary positions at Krita, Treta, Dwarpara and Kali yugas = We don't yet have the capability to know beyond our current Kali yuga start of 3102 B.C. The following site, although a blog, compiles excellent citations for this debate http://bharatkalyan97.blogspot.com/2021/11/kaliyuga-date-18-feb-3102-bce-friday-is.html
To get that figure, you need an ancient genius like Aryabhata who accurately, astronomically measured jyotish astrology with long lost books, and a succession of genius mathematicians. They would need for example; ephemeris with longitude, preferably hour of birth for horoscopes, calculating naksatras, rasi and navamsa.
Due to complex fluctuations of Earth tilt, obliquity, precession and spin speed over millennia, we need computer software to pinpoint accuracy with what we feed it and calibrate it with. Free programme Jaganath Horas is accurate but buggy, Sri Jotish Star software in experienced hands will not function with Greek-based sidereal sky.
So despite a plethora of planetary comments in the vedas, we'd need a.i.nstein (nailed it, coined it) to even begin to see older configurations. There are at least two NASA scientists working on it https://www.vice.com/en/article/wjwmgb/nasa-engineer-who-secretly-practices-astrology
So how do we know we are on the right track today? The calculation must conform to the right traditional calendar, for longer cyclic periods then Puranic time, cross correlating the Vedas and Puranas etc. If we instead try to conform to Christian time (6000 years since adam) it of course falls apart. It May weakly confirm with a geological idea, but it must also correlated with Vedic scripture and chronology.