Welcome to the forum. Please take the opportunity to Introduce yourself and complete your profile so that people can understand how you use ODK.
You have not provided much background here, so I am interpreting your question in the following way:
You have given access to ODK Central to certain users to view (Project Viewer) or edit (Project Manager) data. You separately have data collectors who are able to create submissions either through ODK Collect or a web link (Enketo) - some of the data collectors might be the same as the people who have access to ODK Central.
For Web Users (Project Viewer or Project Manager)
There is not currently a way of restricting access to submissions within a Project or Form within ODK Central (i.e. a sub-set of submissions from one or more forms within a project).
You could potentially work around this by creating a separate Project for each district and then give Web Users access to specific Projects. This would give a web user access to the submissions within that district, and you could give certain users access to more than one project (district) if that is relevant.
However this approach will probably introduce issues for managing data collection and collating data and may not be possible depending on how you use ODK Central (e.g. if you only have access to a single project).
This scenario has been identified by others, so the ODK Core Team are aware of the request for better control of access within ODK Central - they have lots of other requests that they are dealing with too 