Importing Average MPG
 

I'm new to this, but curious if I can import this information.

I've always kept a MPG log in my vehicles, just the date and MPG I calculated by hand. I don't have the actual gallons purchased, miles traveled, or the odometer mileage.

Is there anyway I can import this data into the app?

Unfortunately, not at this time.
The Import process requires the CSV file to have a specific format.
You can see what is necessary here- Importing Your Data Into Fuelly
It includes at the very minimum the data you'd have for a specific fillup (Odometer/Miles Traveled, Gallons pumped, and the date).