That particular functionality is a feature of a Repeating Section Content Control. You would need to actually set up your content inside this type of Content Control.

Which means you need to show your Developer Tab on the Ribbon (Customise the Ribbon) in order to insert a Content Control. If you search for "Repeating Section Content Control" on this forum, youtube or Google you will find useful information to help you figure this out.

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Andrew Lockton
Chrysalis Design, Melbourne Australia