First head over to the products page and view the table of products.
Find the product you wish to generate tags for, and hit the green 'Manage' button at end of the desired product row.
This will load you into a unique product page. From here you can view the table list of all tags currently assigned to the product. See the little red trash can icon at the end of each row. Clicking this will ask for confirmation, and if approved will remove the tag.
We then encourage you to click the big grey button 'Push Tags To Shopify' to make sure all the deleted tags are removed from the product on Shopify too. Deleting a tag initially only removes it from the product in the AI Tagit app