Hello,
There are two ways to solve: Create an attribute and insert in each product one by one.
or Featured products + rewrite the HOT label. So:
1. Edit products in bulk (take one hundred max not to crash the site) https://gyazo.com/877b362983c94844294c6ef10c263bed
2. Set all the products “Featured products” http://prntscr.com/md5ek2
3. Activate the Hot label “HOT” label in the Theme Settings > Shop > Product labels
4. Install free Loco plugin and rewrite “Hot” for “Free Shipping”
You can rewrite all theme and plugin texts via PO file in WordPress. Here is a video tutorial that should help you translate your website texts with a Loco Translate plugin https://www.youtube.com/watch?v=D3NsDdMzsls&list=PLMw6W4rAaOgKKv0oexGHzpWBg1imvrval&index=3
We suggest you to keep translated files in wp-content/languages/themes/woodmart-pt_PT.po folder.
Best Regards