First you have to have good light and a good view, otherwise the reading glasses recommended.
If not of that working you have to put the watch at the front of your camera and try to find it that way.

Here is how I use to do.



And after some training it will looks like this.



This is a service/replacement crystal the have the lying S in the coronet that those crystal have for a few years.
Today it's only the regular without the S that Rolex provides.