To export your exercises, go to the admin section:
Click on the cog icon next to your profile image in the navigation bar on the right.
Select Admin from the drop down menu to go to the administration interface.
In the admin section, in the left navigation, got to Import / Export
At the end of the Exercises section, you can find a download link that exports all your exercises to a CSV file.
As you can see in the screenshot, you can also Import Exercises.