To insert a value into the identity column, you will need to follow this pattern:
SET IDENTITY_INSERT myTable ON
INSERT INTO employee (id, name) VALUES(4, ‘D′)
SET IDENTITY_INSERT myTable OFF
That will allow you to insert a new record with an old ID. However, this is highly discouraged practice. Unless you are re-adding a record that you accidentally deleted or you are adding existing data to a newly-created table, you should really just allow the identity to be created with the next number. Only one record should ever have that identity value. A new record should not get an old (even unused) value.