if you want to create a new item menu, you have to follow the steps in the documentation (Theme Option Panel > General). It’s explained how to create it and how to add the code needed to open it in a new tab.
It is that documentation. The documentation that came with the ThemeForest download. In the menu section on the left, at the point Theme Option Panel > General is explained how to create new menu items that will open in a new tab.
But I can help you. Can you send me your url to check the code? And, what is the menu item you want to open in a new tab?