There's no information on importing custom tones in the Helix manual that I've seen so far.
But I see that there already a bunch of custom tones for Helix on the Line6 site.
I found this video of what needs to be installed on your computer (only MacOS is shown) to update the Helix firmware, view Helix presets on your computer and supposedly to import/export downloaded tones.
I have a Windows 7 PC. I installed the both the Line6 Updater and the Line6 driver2 version. 1.76.0.1. When I open the Updater application with the Helix plugged in I see the Helix and the ability to update the firmware. What I don't see is an obvious way to view presets on the Helix or a way to import a custom tone. Other than the updatable firmware versions there is an option for "Local file". No menu items other than sign out.
Is there currently a version of a Helix editor for Windows? I saw something on this forum about coming soon. Is this the case? Or is there something else that needs to be installed?