[Let's Go] IV Judge System

I need help getting the IV judgement system on Let's Go Pikachu. I didn't know it was a thing until post game and looking up what to do it told me to go east of route 11 and into the house and upstairs to see an assistant of prof. Oak but he's not there? How do I unlock this? Thanks :(

I got it today and I can confirm that there is a prof Oak aide on the second floor of the gate building.