If the string is added in the theme settings, please try the following steps:
1- Go to WPML-> Theme and plugins localization, select your theme and scan it
2- Go to WPML-> String Translation
3- Scroll down and click on the "Translate texts in admin screens »" link
4- Search for the needed string
5- Select the string
6- Click on the "Add to String Translation" button
7- Then click on the "« Return to String Translation" link
8- Translate the string, clear the cache, and check the front end