Hi!
Does anyone know how to enable the warning message when using autorepublish
to a webpage after marked the checkbox "do not show this message again"?

In the help section and on "Office online" you can find help about how to
disable it but not how you enable it again. see the following help text:
------
Help Excel and the Web Basics
Save all or part of a workbook to a static Web page

Control display of the AutoRepublish message
If you don't want the message to appear every time that you save the
workbook, you can select the Do not show this message again check box. Be
aware, however, that this setting then applies to all Excel workbooks that
are set to AutoRepublish.
-------
BR