I personally prefer certain numbers. When I installed Test Flight for the Damus version, my one-tap zaps were pre-determined, it seemed, at 22, which is one of my usual zap numbers. Other than that, I have very little understanding of how to alter that one tap sum. One can go to a profile, click the bolt icon in the upper masthead, and in Wallet of Satoshi, type any value beginning at 1 in order to zap an account.