It is not possible for a software program to identify harmony mistakes because it can't know what you want to do. A "mistake" is what sounds wrong to you. In other words, you need to be able to identify your own mistakes. Some composers want more dissonance, some less.
What you can do is get a software program so you can input your ideas and then listen back. I find it helpful to print out my scores and read them on paper while listening back so I can quickly circle spots I want to change without having to stop the playback.
There are many software programs online. A lot of people I know use MuseScore. I have not used it myself because I use Finale. Finale also has a free version, but the amount of things you can do with it is limited.
If you need help making your music sound better, it is a good idea to get a teacher or mentor who can listen through your pieces with you and make suggestions on how you can improve them. But a good teacher will not force you to change something you think already sounds good, even if they would make a different choice.
Ultimately, you decide what you should fix and what you shouldn't. No program can do that.