You can download the file and open on the script tab inside blender, or copy the text and do like its show in the video
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import subprocess
import sys
import os
# path to python.exe
python_exe = os.path.join(sys.prefix, 'bin', 'python.exe')
py_lib = os.path.join(sys.prefix, 'lib', 'site-packages','pip')
# install opencv
subprocess.call([python_exe, py_lib, "install", "opencv_python"])
# install mediapipe
subprocess.call([python_exe, py_lib, "install", "mediapipe"])