By default, Chargent stores a single payment method (credit card number / token / bank account number) per record that we initiate transactions from the Chargent Orders.
To store multiple payment methods, you would need to create multiple Chargent Orders.
Some Chargent customers also create custom code to store multiple payment methods in another Salesforce object (such as Accounts or a custom object of their own design), and then used apex triggers to populate the payment method for a particular Chargent record when needed.
For this to work, the only requirement is that you insert the correct card/token into the correct fields in the Chargent Order prior to a transaction being initiated. Be sure you are using encrypted fields for storing any sensitive information (any account number data other than tokens, for example).