Can’t change name of labels

Hi,
we are using this amazing plugin with our association and we have some books for children, that we use for activities.
Before this last update I made some changes in the code of the plugin, something really small: i changed the label in “country” with “age” in the front-end page display anche also in the back end add and edit a book. I also changed signed with “available?” and publisher with “where is it?”, so we could locate who borrowed the book or used it.

Now I can’t locate the file wich has the front and back end template, where I can change the labels (just the labels, there’s no problem if the original name of the class remains country or signed).

Where can i change them? which is the file?

Thanks!

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