Ok there is a file with the path
GameData/FerramAreoSpaceReasearch/Plugins/PluginData/FerramAreospaceReasearch/config.xml
open it with a text editor and near the bottom there should be an entry that looks like
<rect name="flight_mainGuiRect">
<xmin>1930</xmin>
<xmax>2160</xmax>
<ymin>587</ymin>
<ymax>901</ymax>
</rect>
and then edit the xmin and xmax fields to move the window back into position, for example my new config looks like
<rect name="flight_mainGuiRect">
<xmin>850</xmin>
<xmax>1080</xmax>
<ymin>587</ymin>
<ymax>901</ymax>
</rect>
scifi6546's post in FAR window was dragged offscreen, How do I reset positions was marked as the answer