Ted here from Shopify, thanks for reaching out to us!
You should be able to add the Newsletter to the footer of your store within the Theme Editor of your admin. Please log in to your admin and select Online Store > Themes > Customize as shown here. Now select Footer. You might need to select Add Content and then Newsletter after that, as shown here. We offer a fantastic Theme Editor tutorial here on Youtube too which I'd recommend checking out for sure!
If there is anything else I can help you with, please let me know, I'm happy to help!
Thanks a mill,