Hello Sean_XiaoEn,

see the manual:
"SIMATIC HMI WinCC V7.5 SP1 WinCC Information System"
"Description of System Blocks"
"User name"

https://support.industry.siemens.com/cs/ww/en/view/109772961/81743352843

Indicates the name of the user (login name):
•The user name is shown the short-term archive list and the long-term archive
list if the user has entered a comment in the long-term archive list and has
changed windows.
•After acknowledgment of a message, the user who was logged on to WinCC at time
of acknowledgment is identified in the operator input message in the short-term
archive list and the long-term archive list. The operator input message must be
activated in WinCC Alarm Control on the "Message Lists" tab

You can display the username in a usertextblock by using the system-placeholder:
@102%s@

"How to specify the text of a message"

https://support.industry.siemens.com/cs/ww/en/view/109772961/89911370891

Regards

Georg Berghof