In general, cost allocation tags cannot be deleted -- they can only be deactivated. If a tag was active and attached to a billing resource at a particular time, it will still show up in cost explorer if the report includes that resource during a period of time in which it was tagged. As for new tags, they should show up in Cost Explorer within 24-48 hours of the tag being created and then Activated on the customer's Billing Console.
However you can exclude the Tag that you do not want in the report (CUR or Cost explore) and only include Tags that are needed
For the tag not listing in the tag editor, you have to use the correct Tag Key and or associated Tag Value. What you can do is that list all resources or the resource that you know, see your CostCenter tag and see how it was tagged, was it under Tag: Name or custom tag key . Also ensure that correct region is selected. Once listed you can click on the tag name and it will provide option to delete. Example if you have used Tag: Name as "CostCenter", you need to use "Name" as tag key and "CostCenter" as value. It will pull up.
Another way to cross check in Tag Editor is select appropriate region, all supported resources, search and then in the search result see how the "CostCenter" tag was used (you can search in Resource search results) . It will be present either under Tag:Name or Tag column.
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