I normally use Audacity 's noise reduction filter. first you record just the noise, ie: you dont speak, just record background noise. then you use that file to create a noise profile in Audacity. By using that noise profile you can try to de-noise your actual recordings. It's not perfect but really helps to reduce noise. For a near perfect result you should use so called ai noise reducers. I dont know anything free out there but all the sites have generous trials you can check, even use for production in some cases. the one i have used is called noise-reducer.com