You will need more than just the APO number to determine where the specific units were located. You also need the unit designation which should be in the line above the APO. An APO number pertains to a whole bunch of units.
APO 29 belonged to the 29th Infantry Division, which was one of the units taking part in the Normandy Invasion in June 1944. The 29th Division's units trained in Scotland and England before the D-Day invasion. If you have the unit designation you will be able to find out more about locations.
APO 230 is Headquarters, 1st Army (not to be mistaken with the fictional 1st Army Group). First Army Headquarters moved into France June 9, 1944. For more reference as to their location you may want to look into the following book - "A Command Post at War: First Army Headquarters in Europe, 1943-1945" by David W Hogan, JR (all 360 pages of it).