For a long time this seemed to me like an esoteric and scary task, but when I had to do it, I discovered that it is not difficult at all. It requires a bit of time, a bit of fiddling, and a tap & die set, but is well within anyone's ability who has full use of their hands. I do not even own this tap & die set, I borrowed it from my cousin! You may have a cousin with a tap & die set too. Many people do.
Cutting oil is available at any hardware store. You can if necessary get away without this but I recommend it. We found, having tried it, that lubrication did two things: it made starting the tap a lot easier, and it made the threads a little tighter so that the screw was not quite as loose in the hole. In fact in a couple cases we needed to use a wrench to get the screw all the way tight! This is not a very big deal either way but I suspect that the tighter screw will last longer.
Step 1: What size?
In our case we had 3/8" screws, and therefore needed to drill holes of 5/16". This information is helpfully printed on the tap itself! The thread gauge for our screw is 16 threads per inch. The tap set had a handy little tool for measuring this, but it is also easily possible to count threads next to a ruler.