If you haven't taken speech therapy, consider taking one. Some common techniques that are taught commonly are 1) stretching first syllable or stretching all vowels (stretching first syllable is more practical imo compared to stretching all vowels Its taught.in an stammering app called stamurai, can try that. 2) speaking in short sentences then breathing then short sentences etc 3) easy onsets/cancellations/pull.outs things.like that 4) costal breathing But it requires extreme dedication and regular practice of atleast 30-40 minute to get better and having a good speech therapist really help.