On something straightforward like that I would probably make a new assembly that contains your assembly only, then do a mirror components on your assembly, making an opposite hand of your current assembly top level only.
If you've generated a new mirrored version of your assembly you will need to make sure you open it from the mirror components feature of the new top level.
You can now discard the new top level assembly.
My preference is to use the generate sub-configurations option rather than mirrored versions.
We have a lot of trouble making opposite hand versions of complicated assemblies with hundreds or even thousands of components, some of which need opposite hand versions and some don't. We've not come up with a great way of doing it yet.