Terminal loop command to change created date for all files in a large directory
I took a stab at writing a script that I think should work for you. You mentioned that you are not too experienced with terminal, so to use it, do the following:


cd into the root of your Movies folder
Create an open a new file (can be named anything, I used change-date) using touch change-date; open -e change-date. This will open a new file in TextEdit.
Copy paste the script below into the open file.
Make the script executable by running chmod +x change-date
Run the script using ./change-date
(Optional) Delete the script using rm change-date


You can replace all instances of touch with echo touch if you would like to test what the script will do. This will cause it to print all of the touch commands it will run, so you can look through the output and make sure it looks correct before removing the echo commands.

#!/usr/bin/env zsh

# recursively loop through all directories in the current directory (should be Movies)
for dir in **/*(/); do
    # use a regex with sed to set $year to whatever is between [ and ] if it is a series of 4 digits
    # if there aren't brackets, or the contents inside the brackets aren't 4 digits, year will be an empty string
    year=$(echo $dir | sed -En "s/.*\[([0-9]{4})\]/\1/p")

    # if the length of year is 4 characters long
    if [[ ${#year} -eq 4 ]] then
        # set the modification time of $dir to Jan 1 of $year
        touch -t "$year"01010000.00 $dir

        # loop through all files in $dir
        for file in $dir/*(.); do
            # set the modification time of $file to Jan 1 of $year
            touch -t "$year"01010000.00 $file
        done
    fi
done


I'm not the most experienced at writing my own shell scripts, but this seemed to work for me. If someone with more experience would like to correct an inefficiency or some other mistake, please feel free.

Before running this script, my directory looked like this:

$ tree -D
Movies
├── [Jan 10 00:22]  12\ Angry\ Men\ [1957]
│   └── [Jan 10 00:22]  12\ Angry\ Men\ [1957].avi
├── [Jan 10 00:22]  12\ Years\ a\ Slave\ [2013]
│   └── [Jan 10 00:22]  12\ Years\ a\ Slave\ [2013].avi
├── [Jan 10 00:22]  13\ Sins\ [2014]
│   └── [Jan 10 00:22]  13\ Sins\ [2014].mkv
├── [Jan 10 00:22]  2\ Guns\ [2013]
│   └── [Jan 10 00:22]  2\ Guns\ [2013].mp4
├── [Jan 10 00:22]  2001\ A\ Space\ Odyssey\ [1968]
│   ├── [Jan 10 00:22]  2001\ A\ Space\ Odyssey\ [1968].mp4
│   └── [Jan 10 00:22]  2001\ A\ Space\ Odyssey\ [1968].srt
├── [Jan 10 00:22]  2012\ [2009]
│   └── [Jan 10 00:22]  2012\ [2009].avi
├── [Jan 10 00:22]  21\ Jump\ Street\ [ALL]
│   ├── [Jan 10 00:22]  21\ Jump\ Street\ [2012]
│   │   └── [Jan 10 00:22]  21\ Jump\ Street\ [2012].mp4
│   └── [Jan 10 00:22]  22\ Jump\ Street\ [2014]
│       └── [Jan 10 00:22]  22\ Jump\ Street\ [2014].mp4
├── [Jan 10 00:22]  28\ Days\ Later\ [ALL]
│   ├── [Jan 10 00:22]  28\ Days\ Later\ [2002]
│   │   └── [Jan 10 00:22]  28\ Days\ Later\ [2002].mp4
│   └── [Jan 10 00:22]  28\ Weeks\ Later\ [2007]
│       └── [Jan 10 00:22]  28\ Weeks\ Later\ [2007].divx



And after running, it looked like this:

$ tree -D
Movies
├── [Jan  1  1957]  12\ Angry\ Men\ [1957]
│   └── [Jan  1  1957]  12\ Angry\ Men\ [1957].avi
├── [Jan  1  2013]  12\ Years\ a\ Slave\ [2013]
│   └── [Jan  1  2013]  12\ Years\ a\ Slave\ [2013].avi
├── [Jan  1  2014]  13\ Sins\ [2014]
│   └── [Jan  1  2014]  13\ Sins\ [2014].mkv
├── [Jan  1  2013]  2\ Guns\ [2013]
│   └── [Jan  1  2013]  2\ Guns\ [2013].mp4
├── [Jan  1  1968]  2001\ A\ Space\ Odyssey\ [1968]
│   ├── [Jan  1  1968]  2001\ A\ Space\ Odyssey\ [1968].mp4
│   └── [Jan  1  1968]  2001\ A\ Space\ Odyssey\ [1968].srt
├── [Jan  1  2009]  2012\ [2009]
│   └── [Jan  1  2009]  2012\ [2009].avi
├── [Jan 10 00:22]  21\ Jump\ Street\ [ALL]
│   ├── [Jan  1  2012]  21\ Jump\ Street\ [2012]
│   │   └── [Jan  1  2012]  21\ Jump\ Street\ [2012].mp4
│   └── [Jan  1  2014]  22\ Jump\ Street\ [2014]
│       └── [Jan  1  2014]  22\ Jump\ Street\ [2014].mp4
├── [Jan 10 00:22]  28\ Days\ Later\ [ALL]
│   ├── [Jan  1  2002]  28\ Days\ Later\ [2002]
│   │   └── [Jan  1  2002]  28\ Days\ Later\ [2002].mp4
│   └── [Jan  1  2007]  28\ Weeks\ Later\ [2007]
│       └── [Jan  1  2007]  28\ Weeks\ Later\ [2007].divx


EDIT ---

To get this answer to work correctly on an external ExFAT drive, a HFS+ disk image had to be created to give the correct permissions. The disk image was created on the external drive and the script was run from that disk image successfully