This seems to be the official website for your monitor. On the right side there is a user manual link that points to a PDF file. If you open it and look for FreeSync, you’ll find that there is a setting to activate that in the monitor menu under Picture > Game Adjust. You have to set it to Extended or Basic to get FreeSync activated. The manual should show you what buttons you should press on the monitor.
Once you have that enabled, it remains to activate GSync on the Nvidia software. For that this article should give you the instructions that you need to follow.
Then do not forget to disable VSync in the Flight Simulator graphics settings to get the actual benefits.
If you manage to do it, respond with a thumbs up to let everyone else know that it worked.