Overall, while it can be incredibly frustrating while you have discharge, your best bet is keeping it as dry as you can. If you can still see some slightly protruding and more sensitive red tissue around the vulva, maybe when you open up your labia, which is where you can use the silver nitrate. You can get 99% applicators off eBay for next to no cost and are useful to have around if you ever get warts on your feet or anything. To use them, have a tissue ready and a glass of clean tepid water. Dip the applicator in the water briefly then drip the excess off over the water before being careful to only touch the over granulation using the mirror. Wipe the applicator with the tissue then bin it.
After using the silver nitrate, putting on some over the counter 1% Hydrocortisone ointment (not cream) on the dried area twice each day until the granulation has gone. It says not to use it on the genitals on the leaflet but that is more so due to the risk of the side effects being increased there. If there isn't anything externally visible, the ointment is also good to spread using your dilator.
Sadly, the science to back this up is weak at best because there are very few studies due to nobody really being willing to fund it. There is however some published evidence of such a treatment being effective around the site of a stoma. Really what you are left to go off is what gets fed back to clinical nursing specialists and word of mouth.
Edit: I should also add that you should try the nitrate treatment once and wait ~3 weeks and increase frequency to a week if you aren't getting any success in terms of it shrinking.
Edit 2: extra clarification regarding evidence that I thought that I should add.