To add walmart affiliate button on the front-end product page. In the Shopify Admin, go to Online Store → Themes, there click on the ‘Customize’ button.

    This will open theme customize page as shown below, Click on Home Page drop down on the top-center.   

    This will open product template selection page as shown below and the template used for product display  

    The Edit page will shown as below, Click on the product information blocks where you want to add “Walmart affiliate button” as shown below  

    After adding the button it will shown as below,  and you can edit button styles also here.