Hey, @SiennaLondon
The grey text there is a design element that is coded into your theme files. You would need to make changes to the theme code in order to do so. I would recommend getting in touch with the developer of your theme in order to see what’s possible on their end. Do you know the name of your theme? If so, I’d be happy to find their contact info on your behalf so that you can get in touch with them.
Otherwise, since I am not formally trained in code to be able to assist you directly but I just wanted to leave an alternative solution. Shopify has an experts platform that allows you to find and hire a developer for small and large coding gigs. With the help of an expert, they could definitely help you do this at a modest cost. If you would like to learn more, feel free to check out our Shopify experts directory.
If there is anything else I can help you with, please let me know.