Is this an indoor grow, or outdoor grow?
Bud rot is next to impossible to eradicate. You might slow it down for a week or two, but you run the risk of it spreading. It spreads through spores, so minimal hand contact is important.
You can spray the entire plant with a potassium bicarbonate water solution. It’ll raise the pH on the buds/flowers/leaves to make it unsuitable to host the fungus. Focus around the area you found rot, but spray everywhere.
If indoors increase air flow and reduce humidity.
@James68 was posting about a wand that could eradicate bud rot, but as far as I know it hasn’t bee proven here.
Either way, I wouldn’t push it for more than another week or so. That damn bud rot takes over quick.