By default, URLs must be unique to each other and can only be used for one specific site. If you wish to re-enable an old URL link assigned to an inactive website and assign it to a current site, you must ensure the URL is not active or currently used. You can quickly visit the site you wish to use and identify if it's still active or not.
In order to reuse an old URL
Make sure that the old URL is no longer active. You may visit the Links & Tracking Dashboard and search the URL there. Once confirmed that the URL is free to use,
Pull up the current site from the Sites & Templates dashboard
Click on Links
Put a check mark on Enable new links to be created
Click on Create a New Link
Enter the subdirectory part of the website link (after .com/)
Click on Create Link
Video Walkthrough