This is all I have been able to locate re his service:

R R. Renick
Residence was not listed;
Enlisted on 7/9/1863 as a Private.
On 7/9/1863 he mustered into "K" Co. MO 7th Cavalry
(date and method of discharge not given)
(Estimated date of enlistment)

Sources used by Historical Data Systems, Inc.:
- Index to Compiled Confederate Military Service Records

……………………………………………………..

R. R. Renick. 31, Private, Capt. C. H. Mobley’s Company, Clark’s Recruits, Missouri Vols.,* joined for duty and enrolled April 24, 1863 in Arkansas by Capt. Edmondson for 3 years or the war, no other records

* This company subsequently became Company K, 7th Regiment Missouri Cavalry, previously the 10th Regiment Missouri Cavalry and Kitchen’s Regiment Missouri Cavalry

Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Missouri