Click on Add Box for the column you would like to add the box to.
Click the Reuse Existing Box tab in the popup window.
Select or fill out the following:
Guide - Choose the guide that contains the box you want to reuse
Box - Select the box you want to reuse
Box Name - If you're mapping this box to the original, you won't be able to change the box title. However, if you're making a copy, you can change the box name.
Position - Decide where your box should appear
Draft mode - if your guide is published, but you're not ready to share this box with the public, use Draft Mode! The box will only be visible in edit mode.
Copy - You will be able to make changes to this version of the box. If left unchecked, you will not be able to make any changes.