Agent code can only be entered one time. Once update the field is now locked and un-editable. 

Though there's a work around to fix this.

1. Login to your HQ Quility account.

2. Click the tiles icon on the upper left side of the page to show all the available apps.

3. Click on Ninja Dialer. This should login to your Ninja Dialer account and automatically update your SFG Agent Code.