If it gets to normal temperature in about 2 minutes I don't think it is the Thermostat.
You need to take the Bottom Radiator Hose off. The thermostat is behind the Water Outlet. Very close to the Oil Filter. 2x10mm nuts hold it on.
I could drive for 30 minutes and the Temperature gauge had hardly moved. Thermostat was stuck open : replaced and all good. Temperature gauge up to normal in 2 minutes.
Could also be the Water temperature sensor. Tells the ECU what temp the water is and turns the idle speed up if it's cold.
Or could be the Idle Speed Control Valve. Tells the ECU when to turn off the Cold Start Injector. You could disconnect the wire on the Cold Start Injector and see if the Idle Speed drops.
Or run the On Board Diagnostics. Read the manual for that one !