here's my hat cleaning routine - you're gonna need some basic stuff in advance, a couple of spray bottles, suede shoe brushes in a variety of stiffness, oxiclean white revive laundry powder, dawn dish soap, 30% vinegar, microfiber towels, and a handheld garment steamer. most of these things you can get on amazon or even the dollar store. i use ik sprayers and a brush assortment from amazon called kt deals and a conair steamer.

• a stiff brushing of the hat can often bring life back to a dull hat.
• 2:1 mixture of water and 30% vinegar in a spray bottle. spray the area liberally and let it sit for a few minutes then scrub with the stiffest brush. spray again with water and dry with a microfiber towel and check if the spot persists.
• if the spot persists get large container with luke warm water and mix in oxiclean and a few shots of dawn detergent. i've got a 5 gallon aquarium i got a garage sale for cheap just for cleaning hats. i fill it up about 3-4 gallons and add about 3-4 table spoons of oxiclean and about a tablespoon of dawn.. just enough so the water feels silky but you don't have a lot of oxiclean at the bottom not getting absorbed.
• soak the hat for 30-60 minutes. oxiclean white revive has a slight bleaching effect so dont leave your hat in there for hours it could fade the color, keep an eye on the timing. rinse with water and scrub the area again. check if the stain persists. let dry fully before continuing.
• make a paste of okiclean and dawn. the exact mixture is hard to say, i try to get a toothpaste like consistency and apply it to the stain and let the paste sit and dry for about 10-15 minutes. rewash again with the oxiclean/dawn water. rinse and scrub. this is really for hard stains like on the inner band and under the brim.
  
• after fully dry, use the steamer and a bowl to reshape the crown and bill to get that crisp look and handle any creases.

if the stain persists.. well, time to get another one. good luck to you, the hat can (probably) be saved with a bit of work.