Adding values to custom form

When we go to below mentioned navigation

1. Define a custom form. Navigation Any HRMS responsibility -> Security -> CustomForm

2. Create a new CustomForm. Form to be customized - select Define User Values from the LOV.

We are able to select Define User Values, However It doesn't allow us to select Define User Table and Columns. Is there a way through which we can add Define User Table and Columns in that lookup.