Hang ziploc bags with water and 3 pennies in it.
Inside or outside?
Here are some tips for indoor flies: https://www.jcehrlich.com/flies/how-to-get-rid-of-flies/
I've also read about the zip lock bag of water with a few pennies in it so I decided to try it last summer. I was amazed that it worked. Wishing you the best.
Home Depot has great fly trap bags which are disposable. It’s amazing how much they collect. Even my neighbor went from those fly stick strips to using the bags.