Here are the corrected sentences:

3. **Last summer, we saw some beautiful lakes in Hanoi.**

4. **Have you ever met anyone famous?** (This sentence is already correct.)

5. **I have lived in Ho Chi Minh City since 2018.**

### Explanation:
- **Sentence 3**: "Ha Noi" should be corrected to "Hanoi" to match the commonly used spelling in English.
- **Sentence 5**: The verb tense should be "have lived" instead of "lived" to indicate an action that started in the past and continues into the present.

3. Last summer, we saw some beautiful lakes in Ha Noi. (This sentence is correct.)
4. Have you ever met anyone famous? (This sentence is correct.)
5. I have lived in Ho Chi Minh City since 2018. (Correction: "I lived" should be changed to "I have lived" because it refers to an action that started in the past and continues to the present.)

So, the corrected sentences are:
3. Last summer, we saw some beautiful lakes in Ha Noi.
4. Have you ever met anyone famous?
5. I have lived in Ho Chi Minh City since 2018.