You can Withdraw an eGC1 that is routing for approval, which makes it editable. Once you have made your changes, click the Route to Reviewers button on the Certify & Route page to re-complete the eGC1 and move it back into the routing process. This will display a pop-up window for you to enter notes about the changes. Make sure your browser is not blocking pop-ups.

For more details, see the Changing a Routing eGC1 user guide article.