To find untrusted foreign key constraints, use this:
SELECT name AS ForeignKey, OBJECT_NAME(parent_object_id) AS TableName, OBJECT_NAME(referenced_object_id) AS ReferencedTable, is_not_trusted FROM sys.foreign_keys
In order to make these constraints be re-trusted, you have to re-check the constraint, so don’t run this on a production system during the day on large tables.
ALTER TABLE TableName WITH CHECK CHECK CONSTRAINT ConstraintName;
The key here is the WITH CHECK. If you omit that the query will still execute successfully, but your constraint still will not be trusted afterwards.