Open all of your doors and windows and use a carpet powder specific for pets before thoroughly vacuuming. Wash ALL fabrics, everything on the beds and all of the drapes in the home etc. Feebreeze does a pretty good job helping with musty smells if lightly sprayed across ceilings and walls. After that you can always paint the walls and the ceilings .too.
Freestanding 2-stage HEPA filter. I’ve three of them, they’re great.
Dehumidifier is essential in the summer. Mine is on a drain hose into the floor drain,
no buckets to empty.
MERV 11 or higher furnace filter.
HEPA vacuum bags.
Eliminate the source of moisture and dampness.
Place Damp Rid products throughout the space. I prefer the ones that are designed to hang in a closet over the buckets. You might need a dehumidifier.
Clean everything with either white vinegar or Odo-Ban.
Newspaper, activated charcoal, and baking soda are also good at eliminating odor. However, Odo-Ban is my go to because I love the clean scent and it also disinfects.
I feel your pain! Here’s what worked for us: https://www.frugalfamilytimes.com/2019/04/how-to-get-rid-of-musty-smell.html?m=1
I used charcoal in bags for getting rid of a smell in our house. You can get it just about anywhere.