Step 1: Find your replacement code within SmartrMail.
Instructions on finding this code are here:
Step 2: Add a success page
This is the page people will see after successfully signing up to your email list. If you leave it blank, people will be redirected to the signup page. If you don't have a success page set up already, you can simply add your homepage.
Step 3: Navigate to the themes section of the Shopify dashboard and click "Edit code"
Step 4: Search for where you signup form is located (This is usually in the footer or newsletter-form liquid files)
Step 5: Replace the <form> action attribute with the SmartrMail action attribute (i.e: "https://go.smartrmail.com/subscribe/XXXXXX") from the first step.
Step 6: Click Save