There is NO way to alter computed column. You have to drop and recreate it.
Let’s say you have a table with 3 column. And the 3rd one is the sum of the other two:
CREATE TABLE MyTable (Column1 int, Column2 int, Column3 AS Column1 + Column2);
If you want to change that computed column as multiply of the other two. Then:
-- First, You must Drop The Computed Column ALTER TABLE MyTable DROP COLUMN Column3; -- And Then You can Create The New Computed Column ALTER TABLE MyTable ADD Column3 AS Column1 * Column2;