In the File Manager's command menu, L click on the F ile item. In the popup menu that appears, L click on the A ssociate item. This brings up the Associate window, where you will see a list of programs that you might use to open a hoc file. But almost certainly it won't, or File Manager would already know about hoc files. B rowse your way to the program that you are going to associate with hoc files.
L clicking on neuron.exe in the list of file names highlights the name of the program.
Then close this window by clicking on the OK button. Now double-clicking on a hoc file should work properly.