You can add your cumulative mileage or expenses manually as a single transaction (for example one entry of 12,340 miles for Jan 1 through Sept 1) and Everlance will adjust for you.
To add data manually, just tap the + sign at the bottom of the app. Be sure to keep your previous records and documentation though!
The most valuable way is to mass import your past Trips and Transactions is to format/upload a CSV file. Click here for instructions!