The only software that can work with old .tcd files from the DOS version of TurboCAD is TurboCAD itself, so if there is any hope for tcd to asat conversion, it will be with the original software. Might not even be possible without manual tweaks or redrawing of the content. In any case, you can always reach out to the TurboCAD online community or support for help.
Updated: August 7, 2023