How to make open external links in the new tab by default?

Is there an option in Atahualpa theme options can do it?

Thanks

sorry I don't understand the question. If you want to add a menu item to an external link, create a wordpress custom menu and add it there

I want to make opening both internal and external inks in a new tab, how can I do it?

There is nothing in the theme that will do this. You might find a plugin that will do it for you.