How can I define the default payment method before generating an invoice by running the Expense Repo

Hello, I would like to define a default payment method before generating an invoice by the Expense Report program How can I define the default payment method before running the Expense Report program ? or how should I configure this? I have other proposition,that can I create a new Supplier Site and define the default Payment Method for this,but the program Expense Report is used for too objectives: expense report and salary of advance . please please I have a deadline for this point, and I'll be appreciate your great help. Thank you again