Can we move back to F2B from F1 category , if yes how , if we send a letter to NVC or USCIS can we send in the opt out request along with our I485 (adjustment of status) , what is the process of opting out of F1 category back to F2B category ?

Yes it can be done. How to do depends on where your case is, at USCIS or NVC. Is the beneficiary in the US?

Yes in the USA , any insight on this

The beneficiary (not the petitioner) can send a written and signed letter to the USCIS office that approved i130 stating that he/she want to opt out of F2B to F1 conversion. Only after USCIS approves to keep it under F2B, i485 can be filed if PD is current based on tables.

U r great bro, already filed I 485 and opt out together and got approved case in contact , she told me she filed it together in 2017 any problem doing this is 2019 , how long does opt out take? How long to receive Yes answer from USCIS?

What kind of letter should we write

Normal letter , how long does it take to get an answer from USCIS ?