Please add the following fields to the Import File Line Item object.
- Payment_CC_Exp_Date_Month (NON RESTRICTIVE picklist, values 01..12)
- Payment_CC_Exp_Date_Year (NON RESTRICTIVE picklist values 2021......2030)
Then while importing assign the values from the CSV / import files to these columns. This will set the Expiry date correctly on the Recurring Payment record.