Keep in mind that some people have had mixed results with this method. It only works if your hairdryer can get very hot and if the label is not that stubborn to remove. The heat of the hairdryer will make the glue dry out and turn brittle. This will make the label easier to peel off. Put a few drops of olive oil into a paper towel, and gently rub any residue spots away. Wash the jar using warm, soapy water to get rid of the oil, then pat it dry with a clean towel.

TL;DR in Vietnamese:
Mở máy sấy ở nhiệt độ cao. Để máy sấy hướng vào nhãn dán khoảng 45 giây. Dùng dầu ô liu để làm sạch phần nhãn còn sót, sau đó rửa với nước xà phòng ấm.