Custom fields set up for tests like the ones below are not available in the Importer utility for mapping to my spreadsheet:
Test Environment (column F)
Test Set (column I)
Test Authority (column J)
Test Browser (column K)
This happens because the "Project" to which you want to import the data would be associated to a screen which have not been configured to these custom field types.
1.Using Jira Administration navigate to <Issues>-><Fields>-><Custom Fields>
2.Scroll to the corresponding Custom field you want the screen to be configured to in the list and click on the cog wheel associated to it as shown in the screen shot below.Click on "Screens" from the dropdown
3.It will result in a page displaying the list of screens and check against the screen (associated with your project) to associate the particular custom field to that screen as shown in the screen shot below
4.Now reconnect to your cloud URL in the importer utility, select the same project and you will observe the missing Test Custom Fields available now for mapping.