If you use the DBCC CHECKIDENT command:
DBCC CHECKIDENT ("YourTableNameHere", RESEED, 1);
But use with CAUTION! – this will just reset the IDENTITY to 1 – so your next inserts will get values 1, then 2, and then 3 –> and you’ll have a clash with your pre-existing value of 3 here!
IDENTITY just dishes out numbers in consecutive order – it does NOT in any way make sure there are no conflicts! If you already have values – do not reseed back to a lower value!