Adding a Custom Text Box to All Product Pages (Using Dawn Version 3.0.0)

Hello,

I’m hoping someone can help me add the necessary code needed to add a custom text box to my product pages. This way my customers can input their specific size directly. I am using the Dawn 3.0.0 free theme template. I’ve tried following other guides to do this, but maybe the code or file has changed for this new version template and is the reason why it isn’t working.

Something that is similar to the picture here is what I’m looking for.

Cheers!