Examine the fieldstone wall for the exact location of the damage. Note the location where the wall appears to bow or lean over. You might have only one small problem spot or have multiple bows and damage.
Measure 2 feet away from the bow and dig a hole. Dig down at least 12 inches. Place a 2-by-4 board into the hole and lean it against the wall. Fill the hole with the dirt you removed and pack it down until it keeps the board from moving. Press down on the opposite end of the board until it sits against the wall.
Repeat Step 2 with any additional areas where the wall leans or tilts to one side. The wood boards will slowly push the fieldstones back up and into the proper support location.
Dig a trench approximately 6 inches deep and 4 inches wide in front of the fieldstone wall. Spray the dirt with water from a garden hose and pack the dirt with a tamping tool until it is flat and smooth.
Arrange a series of larger fieldstones across the bottom. Place the stones between the original wall and the boards. Arrange a second layer of fieldstones over the top, moving the stones so that they sit off-center to the bottom layer. Keep stacking the stones until you have a new wall that is the same height as the wood boards. Remove the boards from the stone and stack more stones until you reach the height of the original wall.
Stand in front of the new wall and push the stones back as far as you can. Press handfuls of dirt against the fieldstone, which fills any gaps or holes between the stones. The combination of new stones and dirt should stop the wall from leaning or bowing.