Crosschecking:
Suppose Sun is in Virgo in the natal horoscope. Then in the Sun’s crosschecking, Virgo is the first house, Libra is the second house, Scorpio is the third house... Leo is the twelfth house.
Do the same for all planets.
The rasi or As crosschecking is the “ normal ” horoscope.
The navamsa crosschecking is the navamsas horoscope, first house is the navamsa sign where the As falls.