First grade teacher - accidentally deleted course for first grade math, how to get it back?

I am a first and second grade teacher. Earlier this year, I set up all my students on Khan Academy with a course mastery goal. One of my second graders just finished the second grade course so I went to go add get ready for 3rd grade to the courses. In doing so, I accidentally deleted the first grade math goal for my first graders. How can I get it back? are all their assignments gone as well?