Box breathing helped me more than anything else getting a handle on my anxiety. Breathe in four seconds, hold four seconds, out four seconds, hold four seconds, repeat until heart rate calms the fuck down and you can get a handle on things. Learning how to quiet your thoughts is big too. Me, I figured out imagining a physical sensation in place of words or images helped. Imagined myself performing a glottal stop then mentally moved the sensation to my brainstem.

It's gonna be frustrating as hell but you gotta mentally experiment and figure out what works for your specific shit. It will be painful. But it is eventually rewarding.