how to add :
git submodule add --force -b master https://github.com/micropython/micropython.git
git submodule add --force -b master https://github.com/micropython/micropython-lib.git
how to re-configure existing submodules:
git config -f .gitmodules submodule.micropython.branch master
git config -f .gitmodules submodule.micropython-lib.branch master