Please use CMSSW_10_1_6.
Download and execute the setup script:
wget -O ${TMPDIR}/checkout_10X.csh https://raw.githubusercontent.com/mkiani/HHZZbb/master/checkout_10X.csh
cd $CMSSW_BASE/src
cmsenv
chmod u+x ${TMPDIR}/checkout_10X.csh
${TMPDIR}/checkout_10X.csh
In the package directory, simply issue
git pull
To commit directly (you need write access to the repository):
git pull
[edit files]
Once you are ready to commit
git pull
git add [files to be added]
git commit -m ["commit message"] [files to be added]
git push origin master