Here are the mistakes with corrections for each sentence:

6. My uncle **runs** around his neighborhood **yesterday** morning.
- Correction: My uncle **ran** around his neighborhood **yesterday** morning.

7. What were you doing while your cousin Kevin **picked** up litter in the park?
- Correction: What were you doing while your cousin Kevin **was picking** up litter in the park?

8. I was writing an essay when my computer **suddenly turns** off.
- Correction: I was writing an essay when my computer **suddenly turned** off.

9. We **were waiting** for the subway to come while it **began** to rain.
- Correction: We **were waiting** for the subway to come while it **was beginning** to rain.

10. The workers **was fixa** the traffic lights all day yesterday.
- Correction: The workers **were fixing** the traffic lights all day yesterday.