Explanation
I found out that I had mistaken the car.
مجھے پتہ چلا کہ میں نے گاڑی کو غلط کر دیا تھا۔
Here 'had' indicates past perfect tense.
We generally use third form (mistaken) of verb in this tense.
First form: Mistake
Second form: Mistook
Third form: Mistaken
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