An actual way to improve your speech is to contact a specialist. I contacted a very good Express Yourself SLP
https://expressyourselfslp.com/ agency. The company's specialists help to get rid of the fear of public speaking, as well as work with speech. In your case, you need to work with pronunciation. The specialist will immediately be able to recognize the cause of the problem and will work individually, depending on the specific case. The duration of the classes is determined by a professional based on your case. I'm sure this will help you!