A voice coach

Who is a Voice Coach?
A Voice Coach - is an acting coach who helps an actor design the voice and speech of a character in the context of a cinematic, stage, radio or animation voiceover production.
His job is to do a research on languages, dialects and their speech patterns, to prepare training materials based on the way languages sound, to instruct and work on lines with the actor.
A voice coach will give the actor feedback focusing on issues of credibility, consistency, and clarity.
In a word, voice coaches teach actors how to imitate a language that an actor doesn’t speak.

Getting Started: 11 Voice Acting Tips
First, you need to find your voice. Sit down and record some lines, then listen to the recording and consider what you can do with it. Think about what you’d like to do with your voice—are you considering narration or acting? How can you manipulate your voice for such?
When it comes to changing your voice, stand straight, drink some water and start working on pitch. Work on changing the volume of your voice, and exercise your breathing (it needs to be controlled). When you hear something you’re going for, take note and work on retaining that voice.

No matter the type of work, you need to speak clearly. When speaking, focus on pronunciation and enunciation. Remember, you need to be clear for the listeners.
A good way to improve your voice is by working with or around others, preferably with a little more skill. You’ll pick up techniques from them, as well as be more motivated to improve your voice and get on par with other talent. Classes from the voice shop in NYC are great for this.

Moving past beginner tips, focus on warm up exercises. Whether you’re working on a demo or have already landed a job, you’ve got to prepare for each session. Get your facial muscles moving, practice lip rolls and breathing exercises, and hum to get warmed up.
On your initial read through for any project or job, don’t simply read through to get an idea of the content. Go ahead and practice your voice any time you read through a script. While we’re on the subject, a few practice reads are always a good measure before recording—know the material!

Keep your voice in shape. In addition to constant practice, from developing your voice or techniques, you need to treat your voice well. Before recording, get some good sleep and drink plenty of water, then run through your warm-ups, of course.
Focus on inflection, which is how you change the form of a word. If you’re reading a statement, avoid changing the tone at the end to sound like a question. It seems like a no brainer, but this happens all the time. In short, your tone needs to agree with the content.

Don’t forget variety. Work with different types of emotion in your speaking and vary specific emotions. Expressing anger doesn’t always have to be loud, express it through emotion rather than volume.
Be theatrical when speaking into the mic. Without debate, voice acting is still physical. By moving your arms and changing facial expressions, the projection of your voice will follow suit. Think of it this way: you need to bring the voice to life.

Don’t rush into creating a demo. Demos cost money and take time, so get the most out of it by mastering your voice prior. You can record and review your voice all you want on your own, but hold up for the demo once you feel comfortable with the voice(s) you’re working on.
Bonus Tip for Voice Acting: Take Classes!

Useful links:
https://youtu.be/a42axivi5Og