Can’t change or rename the category slug? it might be because they are in use by another term. This is a common error in WordPress when adding or renaming the category slug.
If you have checked all tags and there aren’t tags with those slugs then we need fix this error through wp_terms database table in phpMyAdmin:
1. Log in to your cPanel and click the phpMyAdmin Under Databases section.
2. Then click on the Databases tab Located directly underneath the word localhost.
3. If you have multiple WordPress websites you’ll see a list of databases in the right pain. Select the database that you will be working with.
4. If you only have one WordPress website you’ll see one database in the right pain. Select the database.
3. Once you have selected a database, a list of tables appear on the left pane. Locate and click on the table named wp_terms.
4. In the slug column, Click on the word slug on top of the slug column to organize them alphabetically, look for the slug you are trying to create and click Delete.