obvious answer is to push until failure and go agane

more convoluted answer is to see if your tapping technique is sustainable for specific bpm ranges or if you need to change it up a bit (i lift my wrist on 250+ as an example), if not you have to change it according to your needs/genetics, if you think you can push it then its a matter of figuring out your tension, if any, across your entire tapping hand, the forearm is the safest part to tank most tension, but you actually want to balance it out throughout too, fingers, wrist, back of palm, biceps, even shoulder, and then the stamina part is where you push bpms until failure, you can maybe use long stream practice but you're better playing actual maps or the segmented bursty stream maps by ckopoctb/evth, riot1113, seamob, since you're sharing your energy between your aim and tapping hand 50/50 vs 95/5 by aiming a square for 3 minutes, after a while the amount of tensing you have with any part of your arm should lessen once you get used to the bpm, or if you're a player like me that plays pretty periodically, just needs a few hours of warmup and then you're back to where you were