The dreaded answer again, "It depends."
This study: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4918681/
trued Vitamin B12 therapy on two groups of volunteers. SOME people who were deficient in B12 before treatment got some relief. Those who were not deficient did not show improvement. Please note that B12 injections were used in the test.
My experience - I was taking B12 supplements for another reason, and inadvertantly overdosed because they were also in my multivitamin, so my level got too high. There was no improvement in my tinnitus while I was on B12, and no worsening when I stopped all B12 to get levels down.
Please be sure to clear adding a supplement with your doc, excess in anything is not good, and as you can see from the experiment, it wasn't helpful for thos without a deficiency.
Sue