V_NPl , you don't need an attorney to file AP , please use the link below and read the instruction documentation 5 times , should be crystal clear.

All you will need is the form , filing fee , photos and letter stating the purpose of the vist.
They will send you two copies of the AP , I recommend to leave one of them here safe with someone you trust ..just in case you lose the one.

https://www.uscis.gov/i-131