To reenable a disabled user profile:
You need to have *secofr or *secadm as your user class (usually QSECOFR is what people use).
Type WRKUSRPRF and the user profile name to be reenabled. Press Enter. Option 2 by the user profile name and press Enter.
The fourth line down will say "STATUS" *DISABLED. Change this to *ENABLED. If the user has totally forgotten their password, you would type a new password in the second line (User password field), and on the third line change the "Set Password to Expired" parameter to *YES. This will force the user to sign on with their user profile and password the same, but then force them to change it.