PowerShell script for permissions

Hello Folks,

My team came across a situation where we need to fix/assign permissions to folders and subfolders beneath.

Problem statement: There are number of shared folders on servers which are going to migrate to SharePoint soon. We have been asked to assign permissions to users who will be doing the migration. We tried it with PowerShell but sooner faced a blocker. On multiple folders (cannot count as there are so many) we do not have access. 

Our requirement: We are looking for a readymade script or directions using PowerShell where we should be able to identify folders on which our group do not have access and grant us access to those folders. Same script should be able to assign permissions for other users and groups who will be doing the migration.

Note: My team members are part of Local Admin group and can do this manually. But number of folders and in thousands. So doing it manually is not advisable.\

Any quick help in this regard will be much appreciated.

Thanks & Regards

Abhay