Remove default selected variant When used swatches for variant.

[Q_2]

I'm using debut theme. And I want to remove default selected variant from shopify product page. While User click on add to cart button, It should be asked or give error message like 'Please select Size'.

I'm displaying variant using swatches. Please check: https://prnt.sc/xdgq35

And to remove default selected variant, I referred this url:  https://shopify.dev/tutorials/customize-theme-how-to-add-a-pick-an-option-to-drop-downs, but it still not worked.

Can you please suggest me how can I do this?

Please help.