Hi gnedge. Was it sprung on you as an audio task? I had this task first time too but it was a written one which meant of course that I could access the translater before answering, and of course look at all the conjugations too. The tasks pop up randomly and if you were hit with the audio version first then that is unfair... indeed unreasonable. Worth posting it as a problem.
Maybe with continual use daily, Cronder, over some time, you would memorise them. What I do is firstly go to Google Translate French/English and enter the English infinitive, let's use Je Mange but for the conjugation Site I need the French infinite first. So Google Translate gives me for To Eat = Manger. Now I go to Conjugatefr.com click on the link and when onsite I enter Manger and it gives me all 47 of the conjugations. (You won't need all of them to complete the Duo course.) Try it out. Hope it works for you and is useful. Needless to say, eventually, you will need to have at least all the present tense ones of the three groups memorised. Bonne chance. JJ.