What to do after discovering bud rot?

It looks like you may have harvested already? If so, pitch all of the affected stuff for sure and make sure you clean everything extremely well. ATLien415 was kind enough to tell me about HOCL, a cleaner 100x stronger than bleach but safer to use (I've seen that it is used to combat molds/fungi during the grow, and it is sometimes used on food after harvest to prevent rot, but not sure if I would use it close to harvest). That may be something worth considering for cleaning your your tent/equipment/pots/tools/etc. before your next grow. I would also dispose of your soil/media. I had to pitch some branches on one of my plants last year for the same reason, but luckily the rest turned out fine.

Removal of all affected parts is your only option. After that, monitor closely any remaining buds and remove any other ones that develop rot asap. There may be a chance to harvest some clean buds,.........no need to toss the entire plant just yet, but you will need to decrease humidity or increase air exchange to reduce the risk.........but with spores already present, you will need to be a bit lucky too.

throw it the fuck out! lol the first macro pic you can see the hyphea all over. you could try to cut out/prune out around it -- give it a wide berth. But, once you can see 'that' much development, it is already spreading spores. can you save the lower buds? Maybe.. definitely don't dry it with anything else... i'd even use some temporary drying utensils / temp space so as not to contaminate your mesh racks or normal drying room etc. Be generous aobut cutting around where you see infection.. can try to dry what you retain.. if it truns all soft and feels like dry-rot, it's probably infected. You can see that 'netting' of hyphae over the trichomes too. Time will tell if it has colony or not. there is no 'bud washing' that will fix this. lemon, h2o2 whatever.. these people just lie to themselves and later smoke fungi-riddled weed.

Toss it bro, it is not worth it. Live and learn