I think it will help to speak by yourself if you speak while giving yourself positive affirmations, and standing tall while pretending to be in front of an audience. It’s confidence that you want to build up in yourself so you no longer focus on stuttering, but so that you are feeling your strength while interacting with others, and focused on the other person instead of fear. But ultimately I think you gotta get out and practice speaking with people. It’s kinda like, though visualization helps, a sprinter won’t get faster by jogging. So you also need to do the real thing by getting out and interacting with the people that make you feel performance fear