There was a study at Yale - very small study - that found that B-cell depletion therapy resulted in microbiomes that closely resembled the microbiomes of healthy controls than they had pre-treatment.
https://medicine.yale.edu/news-article/gut-microbiome-changes-linked-to-multiple-sclerosis-ms-new-study-finds/
There are some studies on fecal matter transplants but I have been unable to find any medical centers using it outside the context of research.
Here's another study linking gut microbes to MS - https://www.msaustralia.org.au/news/researchers-pinpoint-bacteria-that-may-trigger-ms/