How to Reset WordPress Permalinks
Log into your WordPress Dashboard
In the navigation menu click Settings, then click Permalinks. You will then be on the WordPress Permalinks Settings page.
Notice what setting you have selected, options are Plain, Day and name, Month and name, Numeric, Post name, Custom Structure. If you are using a Custom Structure copy and save it, so you can put it back later.
Select the Plain setting, then click the Save Changes button. If you already have the Plain setting selected, choose Day and name, then click the Save Changes button. You should see a message stating the Permalink structure updated.
Now, select your original setting, and click the Save Changes button again. You are finished when you see the “Permalink structure updated” message again. Your site permalinks should now be working again. You may have to clear your browser’s cache before you see the changes on your site.