Step One

Turn each piece so that the first full tab faces to the right

Hint:

All 4 pieces are identical. If it feels more natural for you, you can simply reverse the pieces and follow the same process with the first full tabs facing left.

Step Two

Starting with the second tab, set one end of the tab into the adjoining slot. Then use your index finger to flex the tab enough to slide the other tab into the slot.
Work your way down the side, then return and set the top tab in place using the same method.
Repeat until you reach the last side.

Hint:

If you have difficulty flexing the tabs, you can use tweezers, or another bending tool, but be careful. Tools are much more likely to crease or damage the tabs.

Step Three

Where the model becomes to narrow to fit your fingers, do the following:
From the outside of the tower, use your thumb to gently flex the tab outward, and use your other hand to guide first the top, and then the bottom of the tab into place.

Hint:

Once you reach the area where the tower begins to flare out again, you can switch back to the original method.