Step 1 was to wrapping the hair around a cardboard box.
Step 2 was to tape the upper edge. I used the narrowest masking tape that we had. It still was a bit too wide so cut in half lengthwise, then applied it very lightly to upper edge.
Step 3 was cutting the bottom of the hair. The flattened cardboard box worked quite well, it was quite easy to slip the end of the scizzors between the cardboard & get an even cut.