Great! Now close the current terminal, and click the Msys2 icon to start a new one. In the newly opened terminal shell, you should be able to run 3DNA commands directly as below:
find_pair -h
That's it!
It helps if you could summarize the steps we have gone through, from a new user's perspective, to improve your understanding of the process and to benefit other potential 3DNA users. In principle, this installation process should not take more than a few minutes for users with some command-line skills. In reality, as you now underwent, it could take much longer, and the process could be quite stressful. It is with such user-support experiences that I've decided to make each of the 3DNA v3 programs (DSSR/SNAP) self-contained.
Best regards,
Xiang-Jun