There are tutors of English and teachers of speech who can certainly help you, but that kind of one-on-one help tends to be pretty costly. Your state or local government may offer free or low-cost group courses in ESL (English as a second language) where you can get much cheaper help with your accent. I used to teach those myself. That is probably your best bet in my opinion. Although in this computerized age there may be online or other automated aids, given that you have been in the US for many years, your problem seems to be that you are not hearing the differences between your pronunciation and that of other American speakers. Maybe today's software is powerful enough to help with that, but I am far from sure. A real human teacher will probably be best for you.