Problem: The client wants to change the source string of a translation while keeping the existing translations intact on their website. Solution: We explained that it is not possible to change the source string directly through WPML, as this is part of the theme or plugin itself. To modify the source string, customization of the source code is necessary, which is beyond the scope of our support. However, for managing translations of strings, we recommend checking the String Translation section of our documentation.
If this solution does not apply to your case, or if it seems outdated, we highly recommend opening a new support ticket. Also, please check related known issues at https://wpml.org/known-issues/, verify the version of the permanent fix, and confirm that you have installed the latest versions of themes and plugins. For further assistance, you can always contact us through the WPML support forum.