'in past' is incorrect on its own. With the clause structure, 'past' is an adjective, which means it needs a noun to complete the clause: 'in past studies' or 'in past years', for example. 'in the past' is referring to something that happened before now. Generally speaking, 'the past' is not very recent, but it's a loose term that means different things to different people. As for 'find vs. find out', there's some overlap in meaning, but 'find out' refers to information that you discovered. 'find' is generally used for physical things, although you can say things like, "I find that carrots make me sick." In that case, 'find' has the meaning 'learned through experience'. Here are some examples: "I found my keys." (physical thing) "I found out that my brother stole my keys." (information) "I found my dog chewing on my shoes." (physical situation) "I found out that my dog likes to chew on my shoes." (information) And here's some overlap, although the meaning is slightly different: "I found that I like French movies." (learned through experience) "I found out that I like French movies." (surprising discovery)

"in past" is wrong. "the" is required in this phrase. However, you might see "past" used as an adjective e.g. "in past times, ..." Research this: https://www.collinsdictionary.com/dictionary/english/find-out and https://www.collinsdictionary.com/dictionary/english/find