Sure! Here are the corrections for the sentences:

1. **If you don’t want to be punished, you would follow the rules.**
- Correction: Change "would" to "should."
- Correct Form: If you don’t want to be punished, you should follow the rules.

2. **Although he was born in Britain, but he is bilingual in Vietnamese.**
- Correction: Remove "but."
- Correct Form: Although he was born in Britain, he is bilingual in Vietnamese.

3. **The exchange student which knowledge of English grammar is excellent is very friendly.**
- Correction: Change "which" to "whose."
- Correct Form: The exchange student whose knowledge of English grammar is excellent is very friendly.

4. **My mum told me whether I was studying or playing then.**
- Correction: No correction is needed. The sentence is correct. (If clarity is needed, "whether" could be replaced with "if," but it depends on the context.)

5. **Have you ever make a handicraft item?**
- Correction: Change "make" to "made."
- Correct Form: Have you ever made a handicraft item?

Let me know if you need anything else!