Hello,
Please go to Theme Options > Styling > Customize buttons > Dark buttons options.
If this doesn’t help, please set for our user Administrator role on your site so we can check settings in the dashboard.
You may change the text of the button using translation files http://prntscr.com/kqsznq or https://docs.woocommerce.com/document/change-add-to-cart-button-text/
Regards