You should always ask your questions that will require discussion in your own new thread. IMO. Otherwise you just cause confusion as to what reply is to whom when they aren't quoted and just makes for a confusing to read thread. Again IMO.

What is this R10 express? Microshift brake levers?

You can put the shifter for the rear on whichever side you want usually. But rear is usually on the right side. I'm having trouble imagining why you say it won't go on the right.

All your Shimano technical documents can be found here....

https://si.shimano.com/


Better details about what you have and are trying to accomplish will help others answer your questions. For me there isn't any detail in what you ask to answer anything but in generalities.

Pics help too if you don't know the exact part number of what you have.