SQL Update - Multiple Columns

update tbl1
set col1 = a.col1, col2 = a.col2, col3 = a.col3
from tbl2 a
where tbl1.Id = 'someid'
and a.Id = 'differentid'

This should work -

    Update Tbl1 
    SET 
    Col1 = B.ColA,
    Col2 = B.ColB,
    Col3 = B.ColC
    FROM
    Tbl2 B
    Where
    B.Id = 'Someid'