How to enter flow state to stop stuttering bc of anxiety?

How to enter flow state to stop stuttering bc of anxiety? I vividly remember a presentation I did towards to end of my senior year of hs where I just entered a flow state and spoke perfectly for the entire presentation, not messing up once. The more I think back on that moment the more I realize that my brain wasn't really doing anything during the presentation. Like I wasn't thinking but I knew what I had to say even though I didn't script anything and that caused my presentation anxiety to just vanish. This led me to realize that my stutter/blocking really only occurs when I feel anxiety about either a presentation, speech, etc. and that "turning my brain off" and entering a flow state was the solution. The problem is I haven't been able to replicate it, my brain always works overtime when I'm presenting or speaking to a group or just new people in general. Anyone have tips on how to kind of choose when I want to go into my flow state? I'm open to taking things like Ashwagandha and L-Theanine because I've heard those help.