吹く: wind blowing and a person blowing on soup
Read the subject in 風が吹く and the object in スープを吹く. Distinguish the seasonal wind from the completed sequence of blowing on soup, cooling it, and taking one sip.
Wind along the river
吹く（ふく） can mean blow. 「春になると川沿いに暖かい風が吹く。」（A warm wind blows along the river in spring.） 風が identifies what blows. This is a warm wind along the river, rather than a person's breath.
春になると sets the seasonal condition, and 川沿いに identifies the location. 吹く here describes wind associated with spring. It is not a past event in which a particular person produced the wind.
Blowing on hot soup
「熱いスープを吹いて冷ましてから一口飲んだ。」（I blew on the hot soup to cool it before taking a sip.） スープを marks the object of blowing, and 吹いて is the connecting form of 吹く. The person blows on the soup; the sentence does not assign the cooling action to the wind.
冷ましてから marks the sequence of cooling before the next action. 一口飲んだ reports taking one sip. 一口 supplies the stated amount, so the action does not become finishing the entire soup.
Following が and を
In 風が吹く, wind is the subject. In スープを吹く, soup is the object of a person's action. Identify what blows and what is blown on to distinguish the two scenes using the same verb.
The river example is set within the recurring seasonal condition 春になると. The soup example gives a sequence of blowing, cooling, and sipping. Preserve those conditions and sequence together with the different subjects and objects.
How do the subject and object of blowing differ in 「春になると川沿いに暖かい風が吹く。」 and 「熱いスープを吹いて冷ましてから一口飲んだ。」?
Show the answer and why
The first describes a warm wind blowing along the river. The second describes a person blowing on hot soup, cooling it, and taking one sip. The wind is not the actor blowing on the soup, and one sip is not the entire soup.