I used to do this on the "Edit Fields" section of a form (where you add and remove columns from a Form), but it looks like there are some updates and this option is no longer available.
If I go to the data sources area, there is an option to refresh the connection, but that isnt picking up the new field. I've even removed the connection all together and then re-added it, but it still wont grab the new fields.
Is there something I am missing or somewhere else to do a full forced refresh?