Investigate for possible causes. Dampness is often the culprit. After I repositioned gutters and made sure we had no leaks, our basement still smelled musty. The fix was a dehumidifier and a fan.
Hire or buy a Steam Cleaner, and do everywhere ceiling to floor, Furniture and fittings, but not electricals! Choose a dry day to do it and open all the windows and doors if possible too. If that doesn't work, there may be a problem with the fabric of the home. Look out for wood infestation or mice or damp issues........ For a quick temporary fix use Febreeze for fabrics.....Shake and Vac for Carpets and Air freshener spray. You could also use cheap Damp collecting gel filled containers from stores and supermarkets...............Good luck!
Here’s how we did it: https://www.frugalfamilytimes.com/2019/04/how-to-get-rid-of-musty-smell.html?m=1
Eliminate the source of the problem. Then use either damprid type products or a dehumidifier. Next, wipe down all surfaces with white cleaning vinegar to kill any mold spores. Finally, OdoBan which is a disinfectant as well as a deodorizer.