The best thing would be to move it to another spot. Unless your whole yard is alkaline. In which case maybe you'll just have to give up on acid-loving plants, unless you are willing to constantly take measures to fight the alkalinity.

Each change in pH point represents a major alteration in the soil environment. Putting on enough acidifier to lower the pH markedly during a short period of time would be quite an assault on the soil community.

While a soil pH of 7 is definitely not ideal for a rhodie, it doesn't mean that you can't grow rhodies in that soil. I've grown rhodies in more alkaline soil than that with nothing more than acidic rhodie fertilizer and composted ground bark soil amendment to adjust the pH.

You won't get the pH down with one application of the sulfur. Just follow the directions as best you can, I don't know what the label says so I can't help you interpret them.

Poor drainage can make a rhodie chlorotic too.