This is the most likely man, but I cannot prove it is the man who was commissioned.
WO338 shows that a 2nd Lt Frank Harrison existed in Warwickshire Regt. .But he is a difficult man to find more on as his commission was on discharge.
1896 Born (from ADRIC register)
1919 Mar 3. Commissioned 2nd Lt in R Warwickshire Regt. The undermentioned Cadets to be temporary 2nd Lieutenants under the provisions of the Royal Warrant dated 30. December 1918, promulgated in Army Order 42 of January 1919:
1921 Mar 3. Joined ADRIC with service no 1798. Posted to C Coy
1921 Apr 2. Posted to Q Coy
1922 Jan 14. Discharged on demobilisation of ADRIC