Start from here: https://www.lexus-tech.eu/default.aspx
then, after registration (for free), go to "owner" section - ECU updates certificates , input VIN of your GS and you will see if some update has been made or not.
Searching in whole site you can verify if there are updates to do for your car: remind that update is NOT a recall, being a recall strongly suggested, while a simple update is often only made if owner finds some anomaly (indicated in corresponding TSB) and he asks to be it done.
Here my certificate indicating fw update:
img002.pdf