After Insert Trigger WIth MS SQL Server I think I have all my bases covered but wanted to ask someone who knows better than I.  This is my syntax.
UPDATE SI
SET autoInsert = 0
FROM inserted
WHERE SI.autoInsert = SI.autoInsert
OR SI.autoInsert IS NULL;

and I want to set autoInsert = 0 where autoInsert = 1 or autoInsert IS NULL
I'm going to assume you have some sort of identity or unique key column on your SI table. (This will be a little more difficult if you haven't.)
I'm also going to assume your autoInsert column is a BIT data type. This means the only values we can possibly have are 1, 0 or NULL. And you want the value updated to 0.
And finally, I'm going to assume you only care about updates to the autoInsert column.
If that's all true, try this:
CREATE OR ALTER TRIGGER dbo.trg_ZeroAutoInsert
    ON dbo.SI
AFTER UPDATE
AS
UPDATE          dbo.SI
SET             autoInsert = 0
FROM            dbo.SI
    INNER JOIN  inserted AS i
        ON      SI.id = i.id ;

If, however, your autoInsert column is an INT (or similar) data type, you can add the where clause to only cover values of 1 or NULL:
CREATE OR ALTER TRIGGER dbo.trg_ZeroAutoInsert
    ON dbo.SI
AFTER UPDATE
AS
UPDATE          dbo.SI
SET             autoInsert = 0
FROM            dbo.SI
    INNER JOIN  inserted AS i
        ON      SI.id = i.id
WHERE           i.autoInsert = 1
    OR          i.autoInsert IS NULL ;