topaz clean is a plugin used in photoshop!
1) download the app, PS Express. (They are both in the App Store and Play Store.) Make an account, you won't be able to use some of the filters/corrections without one.
2) Load up your cover. Go Reduce Noise; play around with the settings. Then Sharpness; play around with the settings — but not too much. And, Clarity if you want.
3) Save, and add desired text in Phonto.