The WooCommerce product editor uses its own editor interface – not the new WordPress Gutenberg interface.
To add a new external image to a product, click Edit Product as you normally would then scroll to where your featured image would normally be. You’ll see something like this:
In the image above, you can see the normal ‘Set product image’ link. Ignore that. Instead paste your featured image URL into the next box, surrounded by a red box in the image above. Once you save the product, External Images will then show you this small preview of the featured image.
Adding Gallery Images
You have two options for gallery images, depending on your preference. You can either paste multiple images into your featured image URL box – separated by commas, or you can keep that as a single image, and paste the other images into the second box provided by the External Images plugin. It does not matter which you do, and it does not matter if you paste them all into both as the plugin will de-duplicate images before displaying the gallery.
So – either paste the gallery images into the second box, separated by commas, or append them to the top box. Use whichever is easiest for you – normally this would be dictated by your import jobs.
If you wish to delete the external images, simply delete the contents of the two boxes for the image URLs and save the product.