I don't really have a special technique; I had engaged in a few formal biofeedback sessions, but ultimately ended up disliking the pain doctor who performed them, as he tried to tell me that my symptoms were real,
not a result of stress (TMS). The neurologist who referred me to him was absolutely furious.
It put a major roadblock in my progress, so I dropped biofeedback entirely for a little while because there weren't many other licensed professionals with availability for me. However, I later began practicing on my own, and experienced fantastic results very quickly. I simply close my eyes and slowly breathe in and out. I have a variety of techniques: I meditate, focus on different parts of my body without fear, or reflect on positive affirmations, my goals in life, happy memories, what happened during that particular day, etc. I make sure to relax my body and all of its muscles, and work toward staying emotionally neutral when looking back on a hard day.
This has made a huge difference in my life. My neurologist was pleased with my progress and said going back to the formal biofeedback sessions isn't really necessary at this point. Had I respected the pain doctor more, I would've gone back, as I truly do believe in what we were doing.
While I haven't used one, apps have helped a lot of people, so I say go for it! It must be noted that believing my overactive sympathetic nervous system (TMS) diagnosis was a
critical component of my overall success. The sympathetic nervous system is
highly responsive to our thoughts and emotions, so make sure to be kind to yourself, and don't feel the need to be perfect when practicing biofeedback. Perfectionism and obsession won't get anyone anywhere! Just focus on replenishing your soul.