Try Google's free online tool.
Type the word you want to pronounce in the search box and "pronunciation in English."
In the screen shot here, you can see I typed
"congratulations pronunciation in English"
You can hear it and you can practice. The computer will tell you if you said it clearly.
(Remember, people are better at understanding you than computers.)
Common Mistake Charts by Language from Ted Power
Look up your language chart to find the most common pronunciation errors in English.
Rachel Smith has a website and a YouTube channel, both full of explanations and exercises to improve pronunciation.
Listen and read along to practice reductions, rhythm, stress and intonation.
Practice hearing minimal pairs with sounds and pictures.
If you like this video from Amy Walker, you may also like her two part explanation of how she teaches herself different accents: Amy Walker: How to Learn Accents