Please clarify, do you need to add privacy policies as a checkbox to subscribe form of your Newsletters plugin?
If so, you can do it easily from Fields tab of Subscribe Forms settings. Simply press “Add New Field” and choose “Checkbox” type: http://prntscr.com/jlylik
Then you can configure it and type required privacy policies to his field: http://prntscr.com/jlym0v
Hope, this information was helpful. Don’t hesitate to ask additional questions.