If you have another Linux desktop computer you could directly read the pi’s SD card to access the necessary file and change it accordingly.
Otherwise If you have an hdmi screen to connect the pi as well as usb keyboard and mouse, it might be easier that way. This will give you direct access to the terminal that will allow you to browse the file system and do some other stuff as well.
Else, the cases above do not apply, on windows you’ll have to download putty to access the pi via ssh, on Mac and Linux you already have a terminal included that you can use.
Googling about ssh and Comand line terminal/interface should give you some basics to understand what it is and how to start using it.
I’ll try to post more details once I have the time to access my pi.
Edit: Also, in the mean time, try searching the forums for similar issue that might have been solved already.