I was reading over something I wrote when I first started writing. One sentences stood out. I thought, it's easy to see this is older material. Not that it was hideously wrong, but it read like I was parroting another author. This is natural. When we first begin writing, we base everything, style, format, voice on things we have read. Since I have established my own writing voice, earlier imitations are easy to spot.
Have you ever noticed when you pick up a book by an author you're familiar with, you expect it to read a certain way, even though there are different characters and situations between the covers? You know this author's voice.
Voice is not difficult. It's you, telling the story as if you were that character. Before you begin a story, you will see certain characters and settings, not always all, generally, a few at a time. As you place them in scenes, watch them, listen to them, how do they react? This gives you the voice of your character.
Don't allow someone else to tell your story. No one will be able to bring your characters to life the way you can.