How to use transmogrify to import csv files into Dexterity content?

Hi, sorry for the late reply.

I would either use mr.migrator as mentioned here:
GitHub - collective/mr.migrator: Mr.Migrator: Drive-by transmogrifiction made easy!

OR
collective.jsonmigrator as mentioned in steps 6 - 10 of my old blog post here
http://www.jowettenterprises.com/blog/plone-content-migration-using-transmogrifier-and-collective.jsonify

(you can ignore the rest as you are not needing collective.jsonify)

Both these methods give you a view on the Plone site where you can select the pipeline you have created (example.cfg or "Example pipeline configuration") from a dropdown menu, and run it. If it's not in the dropdown menu, then somehting went wrong in the earlier steps.