Select the tool that matches the hardware on your chair's hinges. If screws hold the hinges together, select a Philips head or flat head screwdriver. If a nut and bolt combination holds them together, select a hex wrench that fits around the nut.
Turn the chair upside down and rest it on a flat surface so you can easily reach the hinges.
If a bolt is used, grasp it on the inside of the hinge with a pair of pliers to hold it still. Slip the hex wrench over the bolt on the outside of the hinge and turn to the right to tighten it. Continue turning until you have the hinge as tight as possible.
If a screw is used, insert the screwdriver into the head of the screw on the outside of the hinge. Turn the tool to the right to tighten it. Continue turning until you have the hinge as tight as possible.
Repeat with any other loose hinges.