Show me a screenshot of this error.. please. If that command is not there, then your QuickBox has been modified and/or files required by the EcoSystem removed. If you have had QuickBox installed for some time, do you know what version you are running?
You are running a very old version of QuickBox.
Can you preform the following:
apt-get -yqq update; apt-get -yqq upgrade; apt-get -yqq install git lsb-release; \
git clone --recursive https://lab.quickbox.io/QuickBox/QuickBox /root/QuickBox &&
This will rerun the installer on top of your current install. When asked for username/password, please enter in your current master account details. It is normal to say the user already exists.