Arch gives you an amended Form W-4 dated March 9, 2018 on which he claims two additional withholding allowances. He asks you to refund the excess taxes that were deducted from January 1 to March 9 when Arch claimed only one withholding allowance. You should:

Due to the taxes being withheld at a higher rate, you are not able to repay the taxes. Since these taxes were already withheld at an incorrect issue on the company it is not your issue to repay. Arch needs to make the necessary adjustment to the companies annual income tax return when he submits it.