I’m not sure of any way to check it without running it. I’d double check the coolant level, and do the coolant bleed procedure. I believe you need to run the bike for a few minutes until it gets to a certain temp, let the bike cool then check the coolant level again. While it’s running ensure there are no leaks.
Once you do that and top things off, you’ll want to run the bike and ensure it sits at a consistent temp. It might be possible to connect a computer with diagnostics to monitor the thermostat itself but I’m not sure on that.