Trying to add atmosphere as is in the steps of CG Fast Track beginners tutorial step 3. Applied Emission but it looks way too overexposed compared to the tutorial, tried to lower the strength further but made no difference. Any recommendations what I can try to fix this? I'm a brand new beginner to Blender so any help would be much appreciated.
You've connected an emission shader directly to the volume output for the world. With this connection you're saying "emit light from every point in the world" so it pretty much doesn't matter how low you set the light, it's going to be pervasive.
Here I've used a principled volume node and used the density slider to control the amount of fog in the scene, then I made the fog emit just a bit of light.
I encourage you to take liberties with tutorials, because not only did I learn a lot that way, but you'll find yourself creating pieces with a personal touch.