To add additional security instruments you will navigate to the Property Tab and at the top of the page you will want to click "Add Security Instrument". Once you do, that tab will open up for you to fill out the information for the 2nd Deed of Trust. Please note that this scenario must be ordered under Premium support so you will need to navigate to the "Loan" tab and change your current order to Premium to see the above mentioned tab.
To remove the second security instrument prior to submitting the order, please navigate to the bottom of the page of the second security instrument tab and click on the red trash can (see below).
