Don't worry.
别担心。

A：I think you are going to be late for school!
B：Don't worry. I still have a lot of time.
A：我看你上学快要迟到了！
B：别担心，我还有很多时间。

A：I think it's going to rain.
B：Don't worry. I brought an umbrella.
A：我觉得快要下雨了。
B：别担心，我带了雨伞。