You need to have debit customer and credit the bank.
You can creat ethe import of correction journal as follows:
1-Create a new customer payment journal for correction purpose
2-Export the original customer payment journal via entity "Customer payment journal line" and filter against the journal batch number


3-Export the file and then one the file is downloaded, open it and "Cut" the credit values (CREDITAMOUNT) and past them on debit field (DEBITAMOUNT).
4- Update the "JOURNALBATCHNUMBER" which new journal that you have created for correction
5-Delete row for "Voucher" so it will be generated by import
6-Create a import job in DMF, add the entity an upload the file

7-Import the file
Hope it can help you :)