hi how to auto increment for text and char in sql table.?

CREATE TABLE [dbo].[AutoIncrementTest](
  [ID] [int] IDENTITY(1,1) NOT NULL,
  [Range] [varchar](50) NOT NULL,
  [Descriptor]  AS ([range]+ RIGHT('0000000' + CAST(Id AS VARCHAR(7)), 7)) PERSISTED,
  CONSTRAINT [PK_AutoInc] PRIMARY KEY ([ID] ASC)
)

GO

CREATE UNIQUE INDEX [UK_AutoInc] ON [dbo].[AutoIncrementTest]
(
    [Descriptor] ASC
)

insert into AutoIncrementTest (range) values('4MT08C')
insert into AutoIncrementTest (range) values('4MT08C')
insert into AutoIncrementTest (range) values('4MT08C')

select * from AutoIncrementTest