Follow the steps below to add your key on root user.
Step 1: Open the terminal and run the following command on it
A prompt message will appear. Enter yes and continue
Step 2 : Then enter the following in the terminal to enter into editing mode
Step 3: Press i and paste the key which E2E Networks team shared with you. To paste the key press Ctrl+shift+v. Then press ESC and then enter :wq! and hit ENTER to save and exit.