Trying to edit a diagram in libre office

The diagram editor in word used to open a new window that
allowed you to edit the diagram. On closing the window
the edited diagram was present in the word file.

I am trying to edit a document from about 4 years ago
and all I want to do is make a small change to some text in a diagram.
Libre office opens a new window and allows me to edit the diagram.
But what it does is opens a whole new document.
I can save this as a .odt or .png but cannot get it back into the original document.
I am going to re draw the entire diagram with dia, and import it as a png.
This seems to be the quickest route (and the safest for my keyboard (THUMP ARG BA%^&D C%^T etc)).

It depends on the format of the file and embedded graphic. From memory, LO will automatically convert non-native formats to native ones upon opening. Some graphics formats are handled better than others.