If you want all your advertisements to be completely removed from Indeed, go to Settings --> Advertisement and clauses --> Advertisements and turn off the integration with Indeed:
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If you want to remove only one advertisement from Indeed, remove it's publication from your Career site.

To do that, find this particular advertisement and use "Edit on Career page" button to stop posting it (by changing the "end date"), refresh tha page (Ctrl + R) and post it on Career site again.
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