EntityState must be set to null, Created (for Create message) or Changed (for Update message).

I have a Entity object. I try to update and save it using IOrganizationService.

It gives error:

EntityState must be set to null, Created (for Create message) or Changed (for Update message).

This object was returned from another function (not using same context/ IOrganizationService).

I try to set EntityState= Changed but it give other error:

The entity is read-only and the 'EntityState' property cannot be modified. Use the context to update the entity instead.

How to fix this ? it is console app, how to get context ?