For some reason using
cd to blender's python bin folder and then executed command was not working, but ... path to blender's bin folder with python3.7m + command executed at once worked just fine.
Do I have a "pip"?
I don't know if 2.80 was distributed without a pip (as mentioned above), but 2.79 and also 2.83 Mac build containes a pip ... executing
ensurepip was satisfied. You can check that by right click on Blender.app icon > Show Package Contents > Contents > Resources > 2.9x > python > bin, drag&drop bin folder into Terminal window, type
python3.7m -m ensurepip and execute. In my case it looked like ...
/Users/Filip/Downloads/Blender\ 92.app/Contents/Resources/2.92/python/bin/python3.7m -m ensurepip
Terminal recommend update pip to latest version. So copy&paste directory of bin folder or drag&drop bin folder again into Terminal window, type
python3.7m -m pip install --upgrade pip and execute. My example ...
/Users/Filip/Downloads/Blender\ 92.app/Contents/Resources/2.92/python/bin/python3.7m -m pip install --upgrade pip
From what I tried, even without pip care I could just install module by command
python3.7m -m pip install + type your module name. In my case open3d module...
/Users/filip/Downloads/Blender\ 92.app/Contents/Resources/2.92/python/bin/python3.7m -m pip install open3d