The only software that can probably (if even it is possible) to convert .cgr files to .q3d format it would be Quest3D software that uses both of these file types. However specifics about this conversion could not be verified and it may as well be not actually be possible or useful.
Convert Quest3D visualisation scene file to Quest3D project file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert cgr to q3d on Windows
A 3D engine 3D modeling application
Convert from cgr file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.