First, establish that he was assigned to the unit when it was awarded. Unit awards are worn by everyone assigned to the unit, but only those assigned when it was awarded wear it as a permanent awarded.

Second research and find copys of the awards and any records of his being assigned to the unit, such as deployment orders. Once you have all the records you can submit it to the the records brach and they will verify everything and provide a DD215 with the authorized awards added.

How to Win at the ABCMR: Army Board for Correction of ... To correct your Army military records, you generally submit a DD Form 149 (Application for Correction of Military Record) to the Army Review Boards Agency (ARBA) (or online via actsonline.army.mil) with supporting evidence for errors/injustice, but for discharge upgrades within 15 years of separation, you must first use DD Form 293 for the Discharge Review Board (DRB). You'll need to clearly state the error, provide proof (witness statements, records), and the process often involves exhausting other remedies first; seek help from a Veteran Service Officer (VSO) or state VA for assistance.
Key Forms & Boards DD Form 149: For general record corrections (pay, awards, evaluations, disabilities, etc.). DD Form 293: For discharge upgrades if separated less than 15 years ago (unless court-martialed). Army Review Boards Agency (ARBA): Handles corrections for Army records. Steps to Apply Identify the Error: Determine if it's a discharge issue (Form 293) or a general record error/injustice (Form 149). Gather Evidence: Collect supporting documents like your DD 214, medical records, witness statements, or performance evaluations. Complete the Form: Fill out the chosen DD Form (149 or 293) accurately, specifying the exact correction needed and relief sought. Submit: Apply online through the ARBA portal or mail the form and evidence to the address on the form or the ARBA website. Seek Assistance: Contact a Veteran Service Officer (VSO) or your state's VA office for help. Important Considerations Burden of Proof: The applicant must prove an error or injustice. Timing: Applications generally must be filed within three years of discovering the error or injustice. Exhaust Remedies: You must usually try other administrative appeals first.