I found this FAQ and this question is almost the same as I am facing now. 

 I updated user properties using the Identify API. Why are there still “none” values in my charts?

https://help.amplitude.com/hc/en-us/articles/360052385792-FAQ-Modify-or-delete-historical-data

I cannot understand the definition of  “another event” because the target users in my Amplitude account have done some “Events” after uploading the newest UP data from S3 by checking the UserStream charts. 

Using the Identify API only updates user property values for future events. Data that Amplitude has already ingested cannot be changed. The user will have to fire another event in order for Amplitude to apply the updated property value. More details on how user properties are updated can be found here.