“Probiotics:”
Rectally!
They do make vaginal probiotics for recurrent yeast infections. For other conditions....simply taking them by mouth gets where you want them.
But now that you mention it... Fecal microbiota transplantation (FMT) is starting to be a proven treatment. Initially were used to treat C. difficile colitis due to antibiotic use. Takes a fecal sample from a healthy relative (the donor), filtering the sample, and infusing (usually via enema). Several youtube videos on this. Up to 30% get a near complete response per multiple studies.