Remove anything on the chair, such as pillows, a blanket or a chair cover.
Turn the chair upside down and place on a steady surface. A dining room table works well and placing the chair's back over the side of the table will make the chair's seat flush against the table.
Move the chair leg back and forth, side to side to determine where it is fastened and how many fasteners there are. If on a bind, use a flashlight if it's difficult to see. Attempt to move the leg to break the bind.
Inspect the fasteners to determine what type of tool you'll need. Chair leg fasteners can be hex or Allen-head screws, bolts or Phillips-head screws. Retrieve a hand tool appropriate to tighten the fasteners.
Loosen the fasteners first, then turn or reposition the leg into its normal position. Hold the leg against the mounting corner, pressing firmly. Tighten the fasteners securely into place with an Allen-key, socket or screwdriver.
Turn the chair upright and set on the floor. Examine the leg to ensure it is correctly positioned and then sit in the chair to test. The leg should be turned into place.