how to delete notification preview data that existed before the 26.4.2 patch

I understand that with the 26.4.2 patch, when you click on a notification preview to check a text message, the saved preview data is deleted. So, what should I do to delete the preview data that was left over from clicking on notification previews before the 26.4.2 patch?

First of all, I don't want to do a factory reset. So I'm just want to know about this.

how to delete notification preview data that existed before the 26.4.2 patch
 
 
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