How can I do a BEFORE UPDATED trigger with sql server?

MSSQL does not support BEFORE triggers. The closest you have is INSTEAD OF triggers but their behavior is different to that of BEFORE triggers in MySQL.

You can learn more about them here, and note that INSTEAD OF triggers "Specifies that the trigger is executed instead of the triggering SQL statement, thus overriding the actions of the triggering statements." Thus, actions on the update may not take place if the trigger is not properly written/handled. Cascading actions are also affected.

You may instead want to use a different approach to what you are trying to achieve.

It is true that there aren't "before triggers" in MSSQL. However, you could still track the changes that were made on the table, by using the "inserted" and "deleted" tables together. When an update causes the trigger to fire, the "inserted" table stores the new values and the "deleted" table stores the old values. Once having this info, you could relatively easy simulate the "before trigger" behaviour.

T-SQL supports only AFTER and INSTEAD OF triggers, it does not feature a BEFORE trigger, as found in some other RDBMSs.

I believe you will want to use an INSTEAD OF trigger.

All "normal" triggers in SQL Server are "AFTER ..." triggers. There are no "BEFORE ..." triggers.

To do something before an update, check out INSTEAD OF UPDATE Triggers.

Remember that when you use an instead trigger, it will not commit the insert unless you specifically tell it to in the trigger. Instead of really means do this instead of what you normally do, so none of the normal insert actions would happen.

Full example:

CREATE TRIGGER [dbo].[trig_020_Original_010_010_Gamechanger]
   ON  [dbo].[T_Original]
   AFTER UPDATE
AS 
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;
    DECLARE @Old_Gamechanger int;
    DECLARE @New_Gamechanger int;

    -- Insert statements for trigger here
    SELECT @Old_Gamechanger = Gamechanger from DELETED;
    SELECT @New_Gamechanger = Gamechanger from INSERTED;

    IF @Old_Gamechanger != @New_Gamechanger

        BEGIN

            INSERT INTO [dbo].T_History(ChangeDate, Reason, Callcenter_ID, Old_Gamechanger, New_Gamechanger)
            SELECT GETDATE(), 'Time for a change', Callcenter_ID, @Old_Gamechanger, @New_Gamechanger
                FROM deleted
            ;

        END

END

The updated or deleted values are stored in DELETED. we can get it by the below method in trigger

Full example,

CREATE TRIGGER PRODUCT_UPDATE ON PRODUCTS
FOR UPDATE 
AS
BEGIN
DECLARE @PRODUCT_NAME_OLD VARCHAR(100)
DECLARE @PRODUCT_NAME_NEW VARCHAR(100)

SELECT @PRODUCT_NAME_OLD = product_name from DELETED
SELECT @PRODUCT_NAME_NEW = product_name from INSERTED

END