How to alter the function or the table in this situation?

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SQL

T-SQL

Hello.
I have this table in my database :

CREATE TABLE [dbo].[Circulation](
	[Id] [int] IDENTITY(1,1) NOT NULL,
	[Document_Id] [int] NULL,
	[Person_Id] [int] NULL,
	[Librarian_Id] [int] NULL,
	[StartDate] [datetime] NULL,
	[EndDate]  AS ([StartDate]+[Time]),
	[Time] [int] NULL,
	[Delay]  AS ([dbo].[CalculateDelay]([Id],[IsReturned])),
	[IsReturned] [bit] NULL,
 CONSTRAINT [PK_Circulation] PRIMARY KEY CLUSTERED 
(
	[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

and also this function :

ALTER FUNCTION [dbo].[CalculateDelay]
    (
      @Id INT ,
      @IsReturned BIT
    )
	RETURNS INT
AS
    BEGIN
        IF ( @IsReturned = 0 )
            BEGIN
                DECLARE @delay INT = ( SELECT   ( DATEDIFF(minute,
                                                           DATEADD(day, [Time],
                                                              [StartDate]),
                                                           GETDATE()) )
                                       FROM     dbo.Circulation
                                       WHERE    Id = @Id
                                     )
                        RETURN @delay
            END
			ELSE
			BEGIN
			RETURN NULL
			END
			RETURN NULL
    END

my problem is that if I want to alter the function, the following error display :

"Msg 3729, Level 16, State 3, Procedure CalculateDelay, Line 1
Cannot ALTER 'dbo.CalculateDelay' because it is being referenced by object 'Circulation'."

and if I want to remove the formula, this error display :

"'Circulation' table
- Unable to modify table.
Maximum stored procedure, function, trigger, or view nesting level exceeded (limit 32).
"

How can I alter the table or alter the function ?