Currently, Microsoft Word does not provide a built-in option to customize the citation format directly within the referencing tool to exclude the "p." or "pp." before paragraph numbers in the Harvard style citations. The referencing tool is designed to follow specific citation formats, and modifications to these formats are limited.
As a workaround, you may need to manually edit the citation after inserting it. After inserting the citation, you can click on it and edit the text to remove the "p." or "pp." so that it appears as (UNDRR 2015, para 19). However, keep in mind that this manual adjustment may affect the automatic updating of citations if you add or modify references in the future.
For more detailed guidance on using citations in Word, you might want to check the official Microsoft support resources.