Query to insert records from one table into another table based on the column of the first table
You're looking for the PIVOT clause. You can see a working example in this db&lt;>fiddle.

The query is:

SELECT customer_num
  ,p.I AS I_Branch_Code
  ,p.Y AS Y_Branch_Code
  ,p.L AS L_Branch_Code
FROM
(
  SELECT customer_num
    ,Channel_Id
    ,Branch_code
  FROM [table]
)s
PIVOT
(
  MAX(Branch_Code) FOR Channel_Id IN ([I], [Y], [L])
) p