It's pretty easy... Pull it off, and clean the mounts out really well. Get some Window Weld, and make sure the mounting hole is properly-ish positioned. Once you get it, fill in around it with the window weld as completely that you can, making sure to try and leave no air. Let it sit and cure for a day, then put it back in. Wait another day, and you should be good to drive on it.
Should stiffen things up nicely.