Let me know how to edit second and third Tab Pane

I insert a tabs in a container and there are three tabs basically. But I can't access second tab pane and third tab pane. Is there a way I can edit second tab pane? There is no change when I click second tab. There is only first tab pane

How can I edit?

Click on the tab and you should see another little menu at the top where the text editing menu usually is. You will see an open/close button there that will change the current tab content to be edited.

I have no idea why I couldn't see this. Thank you so much!!!