For each category (brutality, technique, survival), you need to touch or hold the top half of its column to increase the value of the category, not press the arrows you see at the top and bottom. Taping or holding the bottom half of its column will decrease the tier value.

Note that the first tap on a tier/column will select it if it is not the currently selected tier. A selected tier is shown by arrows pointing up or down around the tier column and have a selection highlight.