Did you use this method Installing adb and fastboot on a Linux PC to install platform-tools?
On Mint you may require additionally
apt-get install android-sdk-platform-tools-common
and perhaps be in the plugdev group.
sudo usermod -aG plugdev $LOGNAME
The platform-tools install requires you to be able to complete successfully with phone in appropriate mode
adb devices
and
fastboot devices
before moving on to install instructions.