Select the place where you want to install a tie-back on one side of the French door. Tie-backs are often about half way up a French door's height. Mark the installation point with a pencil. Measure to that point from the floor and door frame or glass. Use the measurements to mark the location for a tie-back at the other side of the door.
Place a stud finder over the location where you want to install one tie-back. Move the device from left to right to locate a wall stud. When the device detects a stud, mark the spot with a pencil.
Drill a pilot hole into the wall either 1 inch to the side of the door frame, into the frame or into the side of the French door nearest the wall. If the pilot hole is not in a wall stud, then make it slightly bigger than the tie-back screw. If the pilot hole is in a wall stud, then make it slightly smaller than the tie-back screw.
Push a drywall anchor into the pilot hole if the hole is not in a wall stud. Use a hammer to push the drywall anchor all the way in the hole if necessary.
Screw the tie-back into the pilot hole or the drywall anchor.
Repeat Steps 2 through 5 to install a second tie-back.