Please know that to enable extra product tab we have to follow below steps.

Step-1: Login to your admin panel go to Catalog -> Extra Product Tabs  now at the top you will a + symbol to add the  Tab name.  Please see the screenshot below.  Add the name make the status enable 

Step-2:  Now save it.

Step-3;  Now go to Catalog -> Product and while adding a new product or editing the product at last you will see a tab  Extra Tabs. here you can that extra product tab that you have created in Extra Product Tabs. Please see the screenshot below

Step-4:  In this we have created a Product Video tab, to add the video from YouTube. So click on the YouTube icon to add the video link. Please see the screenshot below.  

Insert the video link.  And Save It

Step-5:  To see the result go the product page for which you have added the extra tab. Please see the screenshot below.