Any legs should be removed.
A Plywood board no smaller than 12" wide x 3/4" thick is installed front to back or side to side, whichever is shorter. Do not cheap out on the plywood, a hardwood Birch cabinet grade is strongest and less flexible. We recommend 16" or more board width. The board is commonly installed so that its center point is 60% back from the chair front edge. Chairs with large heavy backs may require being further back. Every chair is different and may require that after installing, either resetting the board and/or resetting the swivel (forward or back) may be needed to achieve a good balance.
For non-recliner types, install this board at the bottom edges which will raise the chair when completed, 2 3/8". To reduce the raised height, the board must instead be placed INTO the chair bottom. Assemble the Ring and Swivel together using provided flange bolts and nuts. Then twist the top plate of the swivel to resemble a star shape to gain access to the screwholes. Drill a 3/16" pilot through-hole for the provided Phillips head 1" screws and attach the swivel. Alternatively, attach the swivel to the board using 1/4" x 1 1/2" (not provided) bolts and nuts with washers using a 3/8" drill bit.
For recliners, the board may be installed either above or below the steel floor rails. The board probably will be a different size than above due to the many different recliner mechanisms. Check first to be certain the board does not interfere with the recliner mechanism action.