You enter the first one and then add the second one by:

1. Clicking on Business Income and Expenses in the upper left corner. 
2. Click on I'll choose what I work on, on the right.
3. Click Update to the right of Business Income and Expenses.
4. Click Add another business to add the second one. 

Needless to say, you will have to be careful that you don't mix the two up if you go back to edit something.