Show custom message if content is ot already translated instead (migrated content) on custom post type

[fsagaz]

I have installed the plugin on a site that already had a lot of content 'in Spanish.
I selected the second language I needed for my site, English.
I see that it automatically generates the content of the second language from the main language. That is to say, by default in English it puts the content in Spanish.
I see that until I edit the content in the second language in the list of entries the entry does not appear as available in both languages.
My question is, how can I do so that if a user visits an entry in Spanish and changes the language to English, it shows a message like 'content not available' instead of showing the content in Spanish from the English site?