The add-ins have to be downloaded form the Office Store that has to be managed by the administrators manually.That means that every single app has to be controlled if can be used according to the terms of data privacy protection.
In Microsoft OneDrive, various documents are saved, including Word, Excel, Delve or OneNote notebooks. You can easily select this data and save it locally. To do this, open OneDrive, select the documents you need and then click on "Download".
After the saving, you can upload your data to your new area and open it from the various Office 365 products.