Look at the hardware to determine if you have snap hardware. Snap hardware is generally located at the bottom of the furniture. One end of the hardware is a peg that will protrude from the sofa, while the other end has two long toothed prongs that look like an alligator or tuning fork.
Pivot the forked end from beneath the sofa.
Push the sections close enough so the peg lines up between the two prongs of the fork.
Push the sections together. You will hear several snaps as you push. This is the peg snapping past the teeth on the other end.
Push until the two hardware pieces are tightly secured and the two pieces of furniture are aligned.
Look on the side of your sofa to determine if you have clasp connection hardware. Clasp connections are generally in the middle of the side of the sofa sections. One side of the hardware is faces up, while the other faces down.
Push the two pieces as close together as possible. Make sure to line up the pieces so the hardware is touching.
Lift up the section piece with the downward facing hardware several inches and drag it slightly so that it is above the up-facing hardware.
Gently lower the furniture so that the hardware is interlocked. Be careful not to move it too quickly as you can tear the upholstery.