You can fix them your self if you want to.
(1) Stick a toothpick into the hole or more then one. With some glue, this tightens the spot up and the screws hold better.
(2) Drill out the hole and plug it with a Dowel pin cut flush and glued into place.
(3) 2 part Epoxy filled into the hole, Run the screw into the epoxy before it sets up hard. Leave for a minute then unscrew the screw. This will leave threads in the Epoxy, thus causing a solid spot..
Not asing this to be rude, But was the person 2 heavy for the chair? Or had kids beening playing on it? Just trying to figure out why the screw came out? Have not looked ours over as last night was the first time we have used them. We had the kids and grand kids over for Baby Back Ribs and with 10 they were used. LOL
Hope the above helps you or someone out. The Toothpick deal has worked on doors and anyother place with stripped screws for years.