Memorize all starting ticked positions (there's only 4). Then simply tap those (and only those) positions one by one, you'll have everything unticked after you tap the last one.

Caveat:

Works if the number of starting ticks is even.

Proof:

Tapping does not change the state of the tapped checkbox, but flips all others.

There are only two states (ticked / unticked) => If a checkbox is flipped an even number of times, its final state is the same as its initial state. And if a checkbox is flipped an odd number of times, it's final state is the opposite of its initial state.

There are an even number of starting ticks (n = 4). So by tapping all starting ticked positions, we are flipping the rest an even number of times (n), and the starting ticked positions an odd number of times (n - 1).