To fully* reverse it would be to make the cells disappear and be aware you cannot do that with current medications available.
Once the gland has developed you cannot fully* reverse it but you can make glands' atrophy(shrink) slightly from blocking their cell's stimulation with a SERM and raloxifene is notably the best one.
When I utilized it I used 60-90mg daily for a few months.
It helped but wasn't magic.
But be aware the cells have only atrophied so if you resume taking aromatizing compounds and don't control estrogen, it will come right back.