modifying the timestamps of multiple files
The typical way to do this on Unix-based system is to combine find and touch
find path/to/top/directory -type f -exec touch -t 0601120101 '{}' +


path/to/top/directory: top directory to start search in, its content and all subdirectories will be searched. You can add several if required
type -f: only find files. If you also want to touch directories, just remove it
exec ... +: run the command on the matching items (in our case all files), replacing {} with the names of the items.

PS: To just see the files found use find path/to/top/directory.