Tutorial

Set up the shipping bar

Watch the walkthrough, then follow the same steps in your store. More detail is on the documentation page.

Steps

Install Free Shipping Bar Pro from the Shopify App Store.
Open the app. Set the free shipping threshold, three messages, and colors. Click Save.
Click Enable announcement bar. In the theme editor, turn the embed on, preview, and Save.
Optional: use Add block to header instead if you only want the bar in the header. Do not enable both.
Visit the storefront, add a product to the cart, and confirm the remaining amount updates.