What command are you using exactly and what error (if any) are you getting? If the file is stored on Bela in, e.g.: /root/Bela/projects/projectName/file
then running the following command on the PC should work:
scp root@192.168.7.2:Bela/root/Bela/projectName/file ~/Desktop/
(or use 192.168.6.2 if you are on Windows)