This SQL Server procedure encapsulates the process of adding or changing the Description extended property on a table

sql_server_change_table_description.sql

DROP PROCEDURE IF EXISTS change_table_description;
GO

CREATE PROCEDURE change_table_description (
    @table_schema nvarchar(128),
    @table_name nvarchar(128),
    @description nvarchar(255)
)
AS
BEGIN
    -- Validate parameters
    IF NOT EXISTS (SELECT * FROM information_schema.tables 
                   WHERE table_schema = @table_schema AND table_name = @table_name)
    BEGIN
        RAISERROR('The specified table or schema does not exist.', 16, 1);
        RETURN;
    END

    BEGIN TRY
        BEGIN TRANSACTION;

        DECLARE @full_name nvarchar(261) = QUOTENAME(@table_schema) + '.' + QUOTENAME(@table_name);

        IF EXISTS (
            SELECT * 
            FROM sys.extended_properties 
            WHERE major_id = OBJECT_ID(@full_name) 
                AND minor_id = 0 
                AND name = N'Description'
        )
        BEGIN
            EXEC sp_dropextendedproperty 
                @name = N'Description', 
                @level0type = 'Schema', 
                @level0name = @table_schema, 
                @level1type = 'Table',  
                @level1name = @table_name;
        END

        -- Add a table description in SQL Server
        EXEC sp_addextendedproperty 
            @name = 'Description', 
            @value = @description,
            @level0type = 'Schema', 
            @level0name = @table_schema, 
            @level1type = 'Table',  
            @level1name = @table_name;

        COMMIT TRANSACTION;
    END TRY
    BEGIN CATCH
        ROLLBACK TRANSACTION;
        THROW; -- Re-throw the caught exception
    END CATCH
END

sql_server_change_table_description_usage.sql

DECLARE @schema nvarchar(128) = 'dbo';
DECLARE @table nvarchar(128) = 'tripdata';
DECLARE @full nvarchar(261) = @schema + '.' + @table;

EXEC change_table_description @schema, @table, 'new table description';

SELECT * 
FROM sys.extended_properties 
WHERE major_id = OBJECT_ID(@full) 
    AND minor_id = 0 
    AND name = N'Description';