Northern Trust Corporation Customer Service Issues

After retiring from Sandia National Laboratories, my wife and I receive pensions managed by Northern Trust, deposited to Bank of the West. We wish to transfer these direct deposits to our Sandia Laboratories Federal Credit Union account. I found your Address Change/Electronic Deposit Authorization form but it appears more suitable for address changes or setting up EFT, rather than switching an existing EFT to a credit union. Can you provide guidance on how to proceed with this change? Thank you!