You should proceed as follows:
Pull the Bald Cap down at an angle to tense it. Dip a cotton bud in acetone (don't work too wet) and melt a small hole in the Bald Cap at precisely the right place: 2 mm below the point where the top of the pinna (the 'shell' of the ear) leaves the head.
Hint: if necessary, you can melt multiple holes along the line for easy cutting.