how do I open TBC v3.7 with a lower TBC version like v3.6 or v3.4
Ronaldo: It is not possible to open a "newer" version project using an "older" version of TBC. Depending upon what information you are trying to get from the newer version there might be a couple of options.
I have often had to save the data I need as a DXF/DWG and then open that in the lower version of TBC. Just make sure when you export that the "version" is chosen so that the "older" TBC can open it. I have also done the same thing using Civil 3D although this doesn't work as well as TBC's DXF/DWG export.
The other option is to download a copy of TBC 4.12. You will be able to open all prior editions of TBC but, depending upon your license, you may not have full ability to edit the file etc. But viewing, doing basic commands and exporting various file formats and field data is no problem.
Others may have some other workarounds.
Retrieving data ...