Pronunciation is very difficult to correct if you have been speaking English for a long time. As you know, practice does not make perfect, it makes permanent. That means if you practice incorrectly, it will become permanent. You need to correct this problem before moving forward because having bad pronunciation is one of the most difficult aspects of speaking to someone who does not speak English well.
The best way to correct your pronunciation is to find a private tutor. If you cannot afford a private English teacher, then start recording yourself and listen to yourself. If you want to correct your pronunciation problem by yourself, then you have to be very picky.
Here are the things you can do to correct your pronunciation by yourself. First, go to the interview section and pick a long paragraph that has an audio file associated with it. Listen to it several times and read it many times. Read it enough times where you can read it without stumbling. After practicing, record yourself. Listen to yourself, and then listen to the audio file again. Find the words, letters, and sounds that do not sound the same. Correct them one by one. Do not take shortcuts, and do not expect everything to be easy. After correcting everything for that recording, then record yourself again. Follow this step until it sounds exactly the same. Afterwards, go on to the next paragraph and do it again. Keep doing it until you do not find errors.
You’re probably thinking, “You gotta be kidding me!” But rest assured that you don’t have to do this indefinitely. After doing this diligently several times, I promise you that you will see an improvement. Use each improvement as motivation to continue studying and improving.