In most forms, we can add the collection of new fields through attributes.  

In CRM:
  1. Navigate to: Administration > Data > Attribute categories
  2. In attribute categories, click Add
  3. In the dialog box, enter the name of the field you'd like to add.  
  4. Under Record type, select the approperate record type for the form.
    1. Donation Form > Revenue 
    2. Event Registration > Partisipant
    3. User Registration > Constituent
  5. Under Data type, select the type of data you want to collect.
  6. Check Allow only one per record
In BBIS:
  1. Navigate to: Administration > Code tables
  2. Click Refresh code tables

The Form will now have the new field option you created in CRM.