To be clear: The human microbiome contains hundreds of strains of bacteria, often in an established ecosystem. An FMT introduces hundreds of microbes, usually shifting the entire microviome around.

Probiotics aren't incapable of changing the microbiome, it's just that usually they contain only several strains, usually sourced from food or animals, and not humans, in relatively small amounts, and aren't guaranteed to make lasting changes to the microbiome. But they can. If they're the best you can get, they can be worth trying.

Or potentially significant diet adjustments. Having tried to fix my microbiome I have found probiotics useless but the use of prebiotic fibres to promote species does work slowly.

A lot more fun too

Or, something to disrupt the existing biofilms. N-acetylcysteine works for this purpose.