How can I add a parent as a dependent?

I did it by going to DEERS and filled out a simple form. She had to pass a means test. It was easy.

Google DFAS parent dependent, first hit. https://www.dfas.mil/militarymembers/SecondaryDependency/SDC.html

Do your initial research, get with your first line and put together your packet.

"How can I make my parent a dependent? To seek dependent status for an adult family member, such as a father, mother, father-in-law, mother-in-law, stepparent, or someone in loco parentis, DFAS will apply a financial test to determine whether the family member receives over half of his/her income from the Servicemember. You must submit the Servicemember’s or spouse’s birth certificate and proof of the relationship, DD Forms 137-3 and 1172 to show financial dependency, and proof of the family member’s identity to DFAS. For someone loco parentis, this will include affidavits that that person stood in a parental capacity for at least five years prior to the Servicemember (or spouse’s) 21st birthday."

https://home.army.mil/monterey/application/files/5515/4955/2846/How_to_Make_a_Relative_a_Military_Dependant.pdf

https://www.dfas.mil/militarymembers/SecondaryDependency/secondarydependency_Army.html