If you are unable to find the field you are looking for in the standard drop down within 'Choose your data columns' then you might want to investigate the 'Advanced' section:
The drop down 'add a new field' allows you to first select the 'table' where your field lies:
then all the relevant, available fields on that table become available to select:
These fields are listed alphabetically though it may not be obvious from their more code based names which field is the one you are looking for. Please feel free to email in email@example.com if you need assistance in this.
Once you have selected the relevant table and field from the dropdowns you can add it:
The field will then become available to select in the standard dropdown at the bottom of the list: