What do you do if the viewfinder is blurry?
Look through the viewfinder
Don't worry if your viewfinder is blurry, because that doesn't mean there's something wrong with your camera. You can easily solve this problem by adjusting the diopter. Simply look through the viewfinder to adjust the diopter. That way, you can determine when the viewfinder looks sharp to you.
Turn the dial
If you want to adjust the diopter, you can turn the wheel next to the viewfinder to adjust it to the plus or to the minus side. Photographers with both minus and plus strengths adjust the viewfinder to their strength. Make sure to turn the dial until the image of the viewfinder looks sharp. The range of the dioptric correction differs per camera and per brand. Check the manual of your camera for more information about that.