You can enable the Database Form to ensure that the submissions are viewable in a .CSV format. 

Instructions   

1. Navigate to Modules > Content > Forms
   
   
2. Select the category that the form lives in
   
3. Next to the desired form, select Choose an Action > Modify
   
   
4. Scroll down and ensure Database Form is selected Yes
   
   
5. Select Save at the top of the page