I tried to fill the i-821 for tps reregistration.

I went to Nepal on Advance parole on July 2016.
What should I fill on senction below:
4 Eligibility Standard
1 b. I entered the United States on the following date and have
been resided to United states since that time, __________ (mm/yy/dddd)

Please let me know if I need to put this date as when I first entered USA before the earthquake Or I have to enter the date when I entered on USA on Advance parole date.

That's a eligibility criteria to see if you were here during the designation. Put whatever was the last legal entry before TPS

i think both are correct.You can put any date.Any way you are going to send them all proof with advane parole doc copy , approve i81 copy as well as ead.So, it does not matter i guess.