download robomongo 3t from their website. Let downloaded file name is robomongo-0.9.0-rc8-linux-x86_64-c113244.tar.gz
extract robomongo-0.9.0-rc8-linux-x86_64-c113244.tar.gz file
move extracted folder to /usr/bin directory by following command
sudo mv robomongo-0.9.0-rc8-linux-x86_64-c113244/ /usr/bin/robomongo
add export PATH=/usr/bin/robomongo/bin:$PATH in your .bashrc or .zshrc
If you are using fish shell, you need to change the last line to:
set PATH $PATH /usr/bin/robomongo/bin
now start robo3t by typing following in command prompt
robo3t