Frankly, it isn’t really needed.
The camera works very well with the built in macro mode and zoom. It can focus very close, almost on the lens.
That being said, a close up lens may be useful for super macro photos when fully zoomed in.
To mount a macro lens / diopter on the Tough cameras, you will first need a step up ring – 52-67mm, assuming you’re using the Olympus PT-056 / PT-058 / PT-059 housing.
With the step up ring you can mount any of the standard macro lenses available.