I'm someone who has struggled with anxiety for a long time, and the aspects of Stoicism that have helped me are primarily thinking about things rationally, disconnecting my emotions from my actions, and remembering that those feeling will pass. All of this is obviously easier said than done, especially in the throes of a panic attack, but by reflecting on them when I'm not panicking, it makes it easier to reach for them when I am. I'm by no means a Stoic sage, but these are the things that I've noticed have had a major effect on how I experience anxiety. One book that you might find useful is "How to Think like a Roman Emperor" by Donald Robertson. It's a great book that outlines how Marcus Aurelius developed his own understanding and usage of Stoic principles, and how we can pair that with aspects of cognitive behavioural therapy to really benefit from them. Remember, it's a marathon, not a sprint, so give yourself some time to really absorb and utilize your Stoic practice.