Thank you for updating the access I was able to login and reesolve the Contact form success message.
The form used is an elementor form which allows you to add your own success message when the option is enabled.
To resolve I did the following steps:
1. View the ET page in the front end
2. Click on the top bar "edit with Elementor"
3. Edit the ET page directly in elementor and edit the Form element
4. Enable "custom messages" and save
the message was already translated but the option to use custom messages was not enabled in the translation.
