African American Union Civil War Soilder 1863-1865

Seeking information on my maternal gggrand father Warren Brown. I found him about 2012 on a website under United States Civil War Service Record “Union Colored Troops, 1863-1865.  He is also found of the 1870 Federal Census in Terrell, County Georgia. My challenge is when I went to search in the N.A.R.A. I either get  no record found or use Key word search. I tried different wording. I get nothing close.Any information will be greatly appreciated.

Thanks in advance for your attention in this matter.

Ros