Please elaborate more? A quick search is not bringing up much information about how to make a Gsync screen work with AMD cards.
Instructions here. There's a newer version, 1.4.2 which is available on
monitortests.com, not sure if the newer version is necessary or not but you may as well grab the latest. The instructions were easier to follow on Guru3d though.
Specifically to enable Freesync:
Run the app as admin, click on CEA-861 to highlight it then click on the Edit button under the Extension blocks section. Click Add under the Data blocks section and select Freesync range. Set the frequency range in line with your monitors specs (30hz minimum should be fine for most g-sync screens, set the maximum to your screens maximum, so in my case its set to 30hz to 100hz). I also moved the freesync info to the top of the list of "stuff" in the extension window as that was how the example screenshot in the instructions showed it done, not sure if this is necessary. OK the popped out extension box you just edited, then OK the main window and reboot.
If you get black screens or stuttering you need to reduce the refresh range and hunt around for where its going to work. Trial and error it seems. Displayport is the most stable connection method, though hdmi to dp conversion apparently can/does work too. I would imagine cable quality is important, I'm using a good Cable Matters branded DP 1.2 cable. The one that came in the box with my monitor was utter trash and would give me black screens using G-Sync, a decent aftermarket cable fixed that issue and I've been using it ever since.
I think the only gotcha is if you have multiple screens - in that case make sure the correct one is selected in the pull down at the top before you begin, otherwise I don't think anything else needs touching.
I've nothing to do with this app at all, its purely something I found via reddit. I don't know if this works with all G-Sync screens, what needs tweaking if it doesn't work perfectly or anything at all beyond what I've written here. It seems to have just worked for me in limited testing on my other half's pc using an RX480 and two point hospital (yikes!) but your mileage may vary. It would be good to hear of any successes or failures for other forum users benefit.
Good luck!
[Edited instructions, missed some stuff.]