A girl sent a message saying that it was going to cool down, so keep warm. What should I say? I'm not very good at talking.

There are two ways to answer, one is the conventional way: first, you should thank her for her concern, and tell her to pay more attention to keep warm. Then immediately change the subject and talk about something open. The key is that she is interested in the best, so it will be more interesting. The second way is called banter: answer half jokingly and half jokingly. Such as (hey, beauty, I didn't expect to care so much about me? ,,,,) In this way, I won't be so rigid in the question and answer just now.