Changed Query

DO $$
DECLARE
    r RECORD;
BEGIN
    FOR r IN
        SELECT
            tc.constraint_name,
            tc.table_name,
            kcu.column_name
        FROM information_schema.table_constraints tc
        JOIN information_schema.key_column_usage kcu
            ON tc.constraint_name = kcu.constraint_name
           AND tc.table_schema = kcu.table_schema
        JOIN information_schema.constraint_column_usage ccu
            ON tc.constraint_name = ccu.constraint_name
           AND tc.table_schema = ccu.constraint_schema
        WHERE tc.constraint_type = 'FOREIGN KEY'
          AND tc.table_schema = 'fvalue'
          AND ccu.table_name = 'DocumentSection'
    LOOP
        EXECUTE format(
            'ALTER TABLE fvalue.%I
             DROP CONSTRAINT %I',
            r.table_name,
            r.constraint_name
        );

        EXECUTE format(
            'ALTER TABLE fvalue.%I
             ADD CONSTRAINT %I
             FOREIGN KEY (%I)
             REFERENCES fvalue."DocumentSection"("DocumentSectionId")
             ON DELETE CASCADE',
            r.table_name,
            r.constraint_name,
            r.column_name
        );
    END LOOP;
END $$;

ALTER TABLE fvalue."ContractVersions"
DROP CONSTRAINT "FK_ContractVersions_Contract_ContractId";

ALTER TABLE fvalue."ContractVersions"
ADD CONSTRAINT "FK_ContractVersions_Contract_ContractId"
FOREIGN KEY ("ContractId")
REFERENCES fvalue."Contract"("ContractId")
ON DELETE CASCADE;

ALTER TABLE fvalue."Contract"
DROP CONSTRAINT "FK_Contract_Documents_DocumentId";

ALTER TABLE fvalue."Contract"
ADD CONSTRAINT "FK_Contract_Documents_DocumentId"
FOREIGN KEY ("DocumentId")
REFERENCES fvalue."Documents"("DocumentId")
ON DELETE CASCADE;

ALTER TABLE fvalue."ContractVersions"
DROP CONSTRAINT "FK_ContractVersions_Documents_DocumentId";

ALTER TABLE fvalue."ContractVersions"
ADD CONSTRAINT "FK_ContractVersions_Documents_DocumentId"
FOREIGN KEY ("DocumentId")
REFERENCES fvalue."Documents"("DocumentId")
ON DELETE CASCADE;

ALTER TABLE fvalue."DocumentRelationship"
DROP CONSTRAINT "FK_DocumentRelationship_Documents_DocumentId";

ALTER TABLE fvalue."DocumentRelationship"
ADD CONSTRAINT "FK_DocumentRelationship_Documents_DocumentId"
FOREIGN KEY ("DocumentId")
REFERENCES fvalue."Documents"("DocumentId")
ON DELETE CASCADE;

ALTER TABLE fvalue."DocumentRelationship"
DROP CONSTRAINT "FK_DocumentRelationship_Documents_RelatedDocumentId";

ALTER TABLE fvalue."DocumentRelationship"
ADD CONSTRAINT "FK_DocumentRelationship_Documents_RelatedDocumentId"
FOREIGN KEY ("RelatedDocumentId")
REFERENCES fvalue."Documents"("DocumentId")
ON DELETE CASCADE;