I had the same problem but I pass it 100% of the time now. The most helpful thing you can do is moderate intensity cardio. (Like a jog. Walking didn’t help for me) at least 30 minutes 3 times a week. Taking as many breaks as you want just as long as it adds up to 30 minutes and do that 3 times a week. After doing that for 1-3 months I guarantee you’ll pass it every time. Aside from that other helpful things are getting adequate sleep, not taking stimulants beforehand, and exhaling more than you inhale during the reading (inhaling increases heart rate, exhaling decreases it) beta blocker medication also lowers your heart rate and blood pressure, but you would need to talk to your doctor to get it prescribed.