How to change the variant picker to a button that opens a sidebar in the distinctive Shopify theme?

[tomkingham]

How/where in the 'Distinctive' Shopify can I amend the theme to make it so that the product 'Variant Picker' opens a sidebar for choosing variants like engraving i.e. E?

This is the My site I'm working on, and as you can see, the 'Variant Picker' sits on the product page. Instead, I want it to be a button like on the Missoma product page that, once clicked, opens a sidebar for choosing the variant.