Access: Settings -> Shipping -> Free Shipping (Product Based)
A Free Shipping method that will be offered to the selected product that customer purchased.
There are two ways to enable Free Shipping with Product Based.
Access 1: Settings -> Shipping -> Free Shipping
Select Based on Products from Free Shipping Type or Product Based from Free Shipping By.
Title*: The Shipping Name that will appear on your website.
Status*: Enable to live it on your website.
Geo Zone*: The customer location that entitled for this free shipping.
Free Shipping Products*: Select from the category and add selected product that entitled for free shipping.
Show only free shipping: Enable if you wish to show free shipping option only during checkout while criteria is met and hide other shipping methods to prevent customer confusion, provided you have enabled other shipping methods.
Click Save button and Clear Cache to have changes on your website. After that, you can try to make purchase on your website to see if this free shipping is offered on your website.
Access 2: Products -> Click the existing product -> General Tab -> Free Shipping
Go into the individual product and select Yes for Free Shipping. Click Save button and Clear Cache to have changes on your website.