To add the Payment mode:
Go to the "Setup".
Click on the "Payment Method".
Click on the (+) Icon to add the payment type.
Type the Payment name like "Cheque, UPI or cash etc".
Click on Save.
To Edit or Delete the Payment Type:
Simply select the type you want to delete or edit.
Click on the (...) dots >> When the payment type is not in use, click "Delete" to remove it OR click "Edit" to change it.