This tutorial will show you how to reset identity in SQL Server. As you know, Identity column can be used for generating key values.
To reset identity column you can use DBCC CHECKIDENT to manually set a new current identity value for the identity column.
DBCC CHECKIDENT(table_name, NORESEED | RESEED, reseed_value)
The following example forces the current identity value in the ArticleID column in the Articles table to a value of 5, the next row inserted will use 6 as the value
DBCC CHECKIDENT('Articles.ArticleID', RESEED, 5)