Need folders and files under a specific folder to regain all inheritance from the specified folder.
Run the icacls with the recursive and reset switches:
icacls <folder> /reset /t
/t = recursive
/reset removes any modifications from inheritance in the ACL. By default, folders will inherit their permissions from the folder above them.
The final step in this is to give the primary folder that you want to push inheritance from down through the folders the appropriate permissions, all child folders will then have access as intended.