The word "above" can be used as a noun in a couple of limited, and one general way.
It can mean "heaven", "god" or metaphorically "the boss". This is what is meant in your quote. "Our blessings come from god/heaven"
The preposition "above" can also be used a noun elliptically, by removing the noun when the context makes the meaning clear.
Is the aeroplane above or below the clouds?
It is above.
Here the word "above" means "above the clouds", but the context makes it clear.
Dictionaries, especially learner's dictionaries, might not include all the rare senses and uses of a word. But remember that you can never say "above is a noun", only "above is being used as a noun in this sentence". Words only become parts of speech when they are used in a phrase or sentence.