Once you have successfully generated Facebook Page Access Token from ‘Graph API Explorer’, click on ‘Info icon’ from the ‘Access Token’ field. Then, simply go ahead and hit the ‘Open in Access Token Tool’ button.
You will be redirected to the ‘Access Token Info’ page. Right at the bottom, you will find the option to ‘Extend Access Token’. Simply go ahead and hit the button.
Afterward, your Facebook Access Token will successfully be extended. Make sure to keep on extending the Access Token after a certain period of time so that you can carry on using it.