To do any modifications with the form, you have to have at least basic knowledge of PHP. If you plan to record field values in db – then MySQL as well.

Form itself is located here yourdomain.com/wp-content/plugins/authorize_net_payment_terminal/terminal/index.php

You can open that file in your favorite code editing tool and add required form element either

by writing custom code, or just copy paste fields which are already added there. Again, you will have to read the code and understand it. If you don’t have any programming knowledge – please hire somebody to do the modifications for you ( we do provide such service as well, see “request modifications” section