Change ‘submit button’ text to lowercase?

How can I change the submit button text on the site origin form, from uppercase to lowercase?

It’s on this page: http://newsite.advswimschool.co.uk/?page_id=180

There’s nothing in the settings section. I’m still learning how to use WordPress so my knowledge of CSS is fairly limited but I did try looking for the button in the site inspector and adding this code:
.sow-submit { text-transform: lowercase:
}

But nothing happened. Anyone got any ideas? Or do I need to upgrade to the premium version to enable me to do this?

Thanks so much.