Unable to translate the card details – multilingual issue

Hi Team,

Am using WooCommerce Payrexx Gateway plugin for the Credit card transactions.
WPML is used for the translation of the strings.
But not able to find the keys “Test credit card numbers:” and
“Test Amount – Enter a test amount to trigger a specific error response, or leave blank to use the order total.” for translation in String Translation using WPML.

Kindly suggest the solution for the same.