Settings -> Language Learning

If you base language has not changed, hover on the flag to the left of the profile picture on homepage. All the languages you are learning from the same base language will be listed here.

If base language is different, you can click on the Change language option (another flag icon, this time towards the left of the screen). It gives the below link from which you can choose the correct course from a drop down list.
https://www.duolingo.com/settings/direction