If information is not in the public domain e.g. school or hospital procedural documents, anonymise the author and title. For example use ‘Placement school’ or ‘NHS Trust’ in place of the name.
You will need:
Anonymised institution/agency (year) Anonymised title [Confidential document].
NHS Trust (2020) Disciplinary policy. [Confidential document].
In-text citation: (NHS Trust, 2020)