How do I get rid of the musty odor of an old farmhouse?

https://newengland.com/today/living/cleaning/rid-musty-odors/

Try putting out charcoal, and running a dehumidifier. Also damp rid in closets helps.

One product you might want to give a try is called "Room Shocker", which is advertised as an odor-busting solution which uses chlorine dioxide fumes to penetrate through walls and remove any severe odor from various sources such as cigarette and cigar smoke, pet urine, vomit, soured milk, mold, mildew and bacteria etc. It will also decontaminate treated areas of harmful pathogens, spores and fungi that might also reside inside old walls

Open windows to air out the house well on hot, sunny days. Fresh air will make a big difference. Wash any cloth drapes, etc to help remove musty odors. Shampoo carpets to remove mustiness. Generally, clean any surface that can hold musty odors. Then, add small containers of coffee grounds or aquarium charcoal in each room, cabinet space, etc to help absorb odors. Replace as needed until smells have gone away.

I would also put fans in the windows to exhaust and intake air, and keep it moving. https://www.walmart.com/search/?query=window%20fans%20with%20exhaust%20and%20intake&typeahead=window%20fan

I also wash the walls and ceilings, and flooring using Dollar Tree Awesome Orange in 1/2 gal. Get a car sponge, bucket and kitchen gloves while your there.

Thanks you all for your advice.

You can buy air fresheners with charcoal at Lowe's/Home Depot. The charcoal will absorb the idors.