Measure the height between the bottom of the chair frame and the top of the hinged box with your tape measure. Measure the length of the frame box from left to right.
Cut a piece of hardwood to match the height and the length. Use wood at least 1 inch thick to allow for easier mounting. Use a table saw, band saw or scroll saw to cut the hardwood to size.
Drill a pilot hole with a 1/8-inch drill bit through the top of the hardwood block approximately 1/2 inch from each end.
Wedge the wooden block between the chair frame and the hinged box. Double-check that the recliner will not rock backward.
Secure the hardwood block to the hinged box with 2-inch wood screws and a screwdriver.