Determining Which System Values Have Been Changed and By Whom in iSeries AS400

I have Question Related to AS400 in a Healthcare setup, I want to Determine a specific system Value have been Changed and By Whom , For suppose a requisition of a lab test CBC is generated by User ABC but after sometime User XYZ reopens it and overwrites the requisition by changing its default value by "0" (un-post) and saved it again. When extracting data from AS400 the first user ABC name showed who generate the requisition but user XYZ who overwrites it doesn't showed up.

running different reports

Are you probably confusing system values and "simple" database updates?

• System values are global settings for certain aspects how the operating system works. Those usually are only changeable by users with elevated authorities, such as QSECOFR.
• Updates to certain system objects (like database tables) can be tracked by security auditing. This must be configured beforehand. Behind the scenes, a special kind of journal is used.
• Updates to database tables are often backed by journaling, depending on the application being in use. The records created in the journal also track date/time and which user has changed the record in question.
• Any application might be programmed in a way to provide an audit trail. The advantage of this is that this can be tailored to be easily understandable, while the OS provided tools focus on single objects, unaware of the application logic above that layer.

The main difference between security auditing and stock journaling is the scope of which events are tracked. With the links to official IBM documentation, you should be able to learn about those topics.

Bottom line: Can you reproduce who did the change you described above? It depends on what has been configured/used on your system or within your application.