How to Disable Trackback and Pingback from Old WordPress Posts

Click on Posts >> All Posts page. After this select All posts.

Then you have to select “Edit” button from Bulk Actions and click on “Apply” button.

Now a new option will come in front of you in which you will see the pings option. You have to change it to "Do not allow".

Now click on Update button. WordPress will now stop sending pings to your selected posts.