Replacing value in case statement

Hello,

In my dataset each account is assigned to state. In some cases I want to manually adjust the state. I tried to do in in ETL. I created a constant called State with empty string. Then I added a formula tile and created this case statement: (original state is what I had originally assigned to state)

(CASE 

  WHEN `Account'= 'Apple' THEN `State`= 'TX'

 ELSE `Original State`

 end)

Problem is, my Apple account now shows 0 for state instead of Texas, while all other accounts are showing the state copied from 'Original State'

Any thoughts how to handle that?