This is difficult to focus on specifically because there's a good amount of fear on it. You're going to have to make sound (and most likely stutter). That's the only way through it. I would figure out what your mouth/tongue need to do to make that sound and then when you get in a block, don't push but instead drop the tension as best you can and do those things to make the sound. You will stutter and probably feel shame but with time you will get better.