How do I change the manual speed in One Finger Death Punch 2 on the iOS platform?

In One Finger Death Punch 2, it is possible on most platforms to change the game speed by using the +/- keys, or up/down on the d-pad.

The voiceover tutorial in the iOS version of the game also states that it is possible to change the game speed.

However, the aforementioned inputs are not available in the iOS version. There is also no option in the game’s Options screen to change the speed.

I’ve tried tapping and swiping on various places on the screen during a round in attempts to change the speed, but to no effect.

I have found that the game speed will decrease if I intentionally lose a round; however, I’d prefer to not go through a time-consuming process of repeatedly intentionally losing rounds in order to reduce the game speed.

How can the game speed be manually increased or decreased on iOS?