How do I set the focus to infinity?

[mlmPenguin]

I am a very new “photographer” using an EOS R100. Today I tried to take pictures of the night sky, but my camera was out of focus. I tried setting the camera to the manual focus mode in the menu, but I still didn’t know how to actually focus the camera. After doing hours of research and many many tears, I am turning to you guys to answer my probably stupid question. How do I focus my camera?

  

Camera: EOS R100 

Lens: RF-S18-45mm F4.5-6.3 IS STM