Change a string translation without any plugin

Hello there,
i need to change a wrong translation in woocommerce italian language default translation.

The string:
%1$s ending in %2$s (expires %3$s/%4$s)
contained in the template file located at line 53 in:
woocommerce/includes/payment-tokens/class-wc-payment-token-cc.php

In italian is translated as:
%1$s che terminano in %2$s (scade %3$s/%4$s)
But the correct one is:
%1$s che termina in %2$s (scade il %3$s/%4$s)

THE QUESTION:
How can i edit the translation without installing any plugin? I tryed to use the woocommerce.pot file in the languages/ directory. Edited it using Poedit but… i miss someting. Can someone explain me the right procedure?

PS: i also have WPML and string translation installed, but the string is not present in the list under woocommerce domain.