If you do ISPF command ISRDDN, you will see the libraries allocated to your TSO session. Scroll to find SYSPROC ddname.
Are you expecting that each user has their own CLIST library to customize? Be aware that ALL the libraries in the CLIST concatenation must be the same RECFM (FB or VB).
I agree with Dick's question: If you don't even know what the library is, why do you think it must be changed?
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