If you are in a dark place to watch auroras the auto-focus of your camera will not work. There is simply too little light available. To achieve focus there are several options:
– turn off the auto-focus, switch your camera to live view and use the manual focus ring. Once in live view zoom into the frame until there is – for example – a star or the moon. Then turn the manual focus ring until you find that star at its sharpest.
– if the star/moon approach does not work, point a strong flashlight to a tree or rock and use the same live view technique.
– point a strong flashlight to an object (tree, rock, etc) which is relatively far away. Then focus using the auto-focus. After that switch the auto-focus immediately off. This is a good alternative if your camera does not have live view.
– focus during daylight to a far-away object and switch off the auto-focus. Use tape to fix the manual focus ring. This might work well, but be sure to test it out.
Remember to always check the photos you captured if they are as sharp as you want to. If not, adjust again

Manual focus ring