I don't have experience with these, but often people name one of these therapies/therapists: SLP stephen, Tim Mackesy, William Parry, MCguire program, toastmasters and Broca Brothers. The last one 'broca brothers' are two brothers who outgrew/recovered from stuttering when they were adults. They have YT videos how their trial and errors strategy works. I have not yet wrote a summary on their strategy unfortunately but I did watch all their videos