I accidentally changed my git diff tool and it was not actually installed and I have no permissions over the machine. How can I revert to the original tool that shows changes in command line? It may sound silly but I have not been able to make a single diff and I have found no information about this, only on how to change it to others than the default. I have tried to unset the variable but it doesn't work.
This depends on how you changed your git diff tool config when run
If you used --system, your configuration will be write to system-wide $(prefix)/etc/gitconfig
If yur used --global, your configuration will be write to write to global ~/.gitconfig file
Try to find diff.tool configure value in above files and delete it.