If you have a confirmed cases of coronavirus in your setting (staff member or a child), or you’ve been advised to close as a result, you should tell Ofsted as soon as is reasonably practical, and in any case within 14 days.

Please have a look at the guidance on reporting incidents to ensure you include all of the information required: https://www.gov.uk/…/report-a-serious-childcare-incident

You can report online via the link above.