Currently, the Mass File Migrate app is designed to be installed in the source org. From there, you can initiate and manage file migrations to the destination org. At this time, the app does not support installation in the destination org to initiate migrations.
PS: View Mass File Migrate Salesforce file migration app on Salesforce AppExchange:
https://appexchange.salesforce.com/appxListingDetail?listingId=e9874a66-2001-4e3d-8a29-3a2ed7f584c4