copy an updated field to another field automatically by CREATE TRIGGER

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SQL-Server

Hi, I'm using sql server.

there's a table with some fields: column1, column2, ...

the user has access to column1, and he can update it's content.
Now I want to create a trigger to copy the new content of column1 to column2 automatically.

e.g. set column2 = column1 AFTER UPDATE (column1)

I've created a trigger on the table. in the trigger I use the code bellow:

CREATE TRIGGER [dbo].[mytrigger]
   ON  [dbo].[mytable]
   AFTER UPDATE
AS
IF UPDATE(userName)
BEGIN
    
    SET NOCOUNT ON;
    
    -- HERE I SHOULD WRITE A CODE TO COPY NEW DATA OF COLUMN1 TO COLUMN2 !! :-??

END

WHAT code should I use instead of the comment ??

I'll appreciate any help.