What do I have to do with the ZIP-File ??

Extract the ZIP-File to a temporary directory.
You will get the following 4 Files:

cwbsomr2 dll        27.648  15.03.99  12:31
cwbsomr3 dll        19.968  15.03.99  12:31
cwbsomr4 dll         6.144  15.03.99  12:32
cwbsomr5 dll         7.168  15.03.99  12:32

Close Operations Navigator.

Put these files in the subdirectory MRI29xx of the path where Client Access is installed.
(e.g. C:\Programme\IBM\Client Access\MRI29xx)

Restart Operations Navigator.