How to add --dev /path/to/device to the start line?

hey guys, my phoscon break after beta update and I saw on github the solution:

For users looking for a work around:
Adding --dev /path/to/device to the start line make it work again.

But I cant find nothing about the start line, how to edit and where it is?

Thank you guys

@senilio was nice enough to write some more detailed instructions