Cambridge Dictionary gave the following rules that will help us learn how to use “above” and “over”.

A. When we use above as a preposition, it means ‘higher than’. Its meaning is close to that of the preposition over. In the following sentences, over can be used instead of above.
Example: The waves came up above her head and she started screaming. (or … came up over her head …)
– We use above, but not over, to refer to things that are at an upper or higher level.
Example: Do they live in that chalet above the village?
– We usually use above, but not over, when there is no contact between the things referred to. Over or on top of have a more general meaning, and can be used when one thing touches or covers another.
Example They made her comfortable and put a blanket over her.
B. We normally use over not above with numbers.
Example: I get over sixty emails a day.
– When we talk about temperatures in relation to zero or (the) average, we use above not over.
Example: It was three degrees above zero.
– When we refer to temperatures in other contexts, we can normally use above or over.
Example: The temperature is already above 30 degrees. (or … over 30 degrees.)
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