Do you have any additional information on your relative? Name, DOB, place of birth?
Hello Ms. Murphy,
Thank you for contacting History Hub!
The National Archives does not hold the records for Confederate service. However, if you know what state your ancestor was from you should contact the state’s archives by visiting the National Archives page on Confederate Pension Records for the state contact information.
For information regarding serving in the Union after becoming a “galvanized Yankee” then it would be best to start your research on the Civil War Records: Basic Research Sources page. The next step would be to search the Compiled Military Service Records and the General Index to Pension Files, 1861-1934 available on Ancestry.com for a fee. Some public libraries do have access to this subscription site.
Best of luck in your research!