Couldn't found or Couldn't find?
For example, my mom asked my to find the car key, I've checked properly and I replied to my mom I "couldn't find" in my room OR I "couldn't found" in my room?

Question

Answer

couldn't find it in my room :)

Find is infinitive and found is past tense.

Answer

The answer above is spot on. To give an example:

I couldn't find my keys.             Find--infinitive
The keys couldn't be found.     Found--past tense