Our third cover tutorials is the one I showed above.
Open your blank template (635x1000) and tap the "SHAPE BUILDER" icon below. The one with the circle and overlapped by a square icon.
Tap the square shape and click "STROKE" (as shown above) and then change the size to 15 and then tap OK.
Stretch your square until it becomes a border of your blank template. And then tap "DONE".