DropDown plugin is dynamical action plugin (turns standard region button into dropdown button), that means you need to :

1) create standard button
2) create dynamical action on Page Load
3) create action under true and select "Action : dropdownButton"
5) under Settings

• choose Type (for example Page numbers) and select your pages for navigation or enter list of pages with comma separator (for example 2,3,4)
• under Affected Elements -> Selection Type chose Button option and then select your button