To Revert Customizations made to Selected Ribbon Item

Note: This procedure works only for customizations made to the tabs and groups delivered with the product.

Do one of the following:

Select File > Settings > User > Customize Ribbon .

or
Right-click in the blank space in the ribbon and select Customize Ribbon from the pop-up menu.

The Customize Ribbon dialog opens.
In the Customize the Ribbon list, navigate to the customized tab or group whose customization you want to revert.
Do one of the following:

Right-click and select Revert.

or
Click Revert > Revert customization for selected Ribbon Item.
Click Apply.