In the Gallery tab, you can add, delete images and alter the order they are shown on Single product page.
To make changes to pictures, use Image Editor, the built-in editing tool. Click the pencil icon to start editing.
Click the eye icon to preview image:
Click ALT to add alternative text for the image:
Click the trash icon to delete image:
You can easily change the featured image by clicking Featured:
'Add image from URL' option
Enter image URL like: https://www.camerasafrica.com/wp-content/uploads/2018/12/Phottix-3-ring-macro-extension-tube-Auto-focuscanon-1.jpg and image alternative text→ click Add image, and it will be added to the Gallery:
'Add image' from your computer option
Click Add image → select the image from your computer → click Save changes.