While I can't guarantee a microbz product will cure the Rhinosinusitis, I can say that good gut health is the foundation of 90% of our health and so starting there is a great thing to do.
All the beneficial microbes in our body play a role in all its systems including the mucous membranes.
If there was any link with allergy to this then strengthening the immune system with microbz is also beneficial. Netti pots can also help, especially to soothe or decongest, and you can put a little of the microbz in with the water too.
I highly recommend the book Breath by James Nestor - these things can be changed at any age.