I-539 for B2 extension gap while waiting for COS to be approved

[Vishal2019]

I just filed I-539 for the COS. Now I have to file for the same again to bridge the gap while waiting for the COS approval, at part 3, I/We request that my/our current status be extended until (mm/dd/yyyy). What date should I enter? How can I provide the reference for the already filed I-539 for change of status from B2 to F1? And how do I know that when I have to file the I-539 again for the bridge gap and how many times?
I mean every 6 months or each time my SEVIS start date differs?
Thanks in advance.