If you are trying to add or import something into Magento 2 and get the error "The value specified in the URL Key field would generate a URL that already exists", here is one way to fix it. First, do not try to add a new redirect by clicking on the HTML file name in the error. Usually, it does not help.
- Backup your Magento database
- Open Magento database (in SSH, phpMyAdmin or another database manager)
- Find and remove the records with the HTML file name listed in the error from the table called "url_rewrite"
For example, if the URL listed in the error is "paulownia-hand-carved-pumpkin-large.html", you run this MySQL command:
delete from url_rewrite where request_path like "%paulownia-hand-carved-pumpkin-large.html"
but an easier way is to submit a ticket to our support team with the list of URLs in the error you received and we will fix it for you.