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It appears to be a soil infection. Fungal infections can be treated, though. I recommend wettable sulfur, or essential oils such as: lavender, cinnamon, and garlic. Neem oil also helps in these cases.

Refer to the article below to determine if your new tree is planted in the proper soil and growing conditions.

https://www.gardeningknowhow.com/ornamental/trees/colorado-blue-spruce/care-for-colorado-spruce.htm

Newly planted trees need regular watering to ensure it can become established before dormancy and winter.

Watering amounts will depend on the size of the new tree, soil conditions and environment.

Some needle drop is normal for a Colorado Blue Spruce.
If the condition worsens and the tree shows other signs of stress, it could be due to disease.

https://www.extension.iastate.edu/harrison/news/common-diseases-blue-spruce

This link has watering guidelines.
https://ask.extension.org/questions/184569

Remember that most garden centers or greenhouses guarantee a new tree for 1 year from purchase.

Typically, what you would do instead of fertilizer, would be to mulch the tree with organic matter, or compost. They don't, generally, need a heavy fertilizer. Here is an article with more information: https://www.gardeningknowhow.com/ornamental/trees/colorado-blue-spruce/care-for-colorado-spruce.htm

Unless you are seeing webbing, I would not say that this is a case of spidermites. The damage from this pest is very clear. If I had to guess, I would say this problem is either a pH issue, which can cause many problems in itself, or a fungal issue. Either way, You can cure both problems at the same time. Use dolomitic lime to ensure the stability of the pH, and iron sulfate to add just a touch of acidity, and kill off any bacteria, or fungus in the soil.

To be safe I would wait until spring. These are hardy in your area, and will survive just fine outdoors. I would just wait until spring to give it the best chance to recover from transplant. Here is an article that will help: https://www.gardeningknowhow.com/ornamental/trees/colorado-blue-spruce/care-for-colorado-spruce.htm

Look for a slow-release fertilizer labeled for pines or evergreens. Most soils have sufficient phosphorus although you need a soil test to confirm this. You are mostly looking for a nitrogen source and a bit of potassium. Several inches of rich compost would do. Here is an article from Univ of Minn Extension Service: https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/fertilizing-evergreens-conifers/