You have to make sound. Sound you don't want to make. You create different sounds by moving the parts of your mouth that make them (jaw, tongue, lips). Nothing is preventing you from making these movements other than the conditioned blocking response and fear/shame/etc. To work on this you need to start in the easiest or safest situations where you may still block and where you can get yourself to a chance. You're going to have to play around with it and figure out where you can do this. It may take a while to be able to do it if you keep taking it one step at a time you will slowly get better. Once you can make a sound, the next step is to move to the next sound. Don't push.