How to Bulk Update Order Header level EFF on existing sales orders in the system

Summary:

We have business requirement to update/change ATTRIBUTE_CHAR8 Header EFF value for all Open Sales orders.

Kindly let us know correct approach to achieve this business requirement.

We have tried 2 approaches in lower Instance:

1. Using FBDI --> getting error: while importing from interface table to base table.

2. Using Rest API -----> getting error: 401 unauthorized.