Can't upgrade my 2017 Macbook Pro

I need to upgrade my OS as I took my 2017 macbook pro into an Apple Store due to a battery issue. They told me I need to upgrade to the latest OS as the battery needs a firmware update. However, when I try to check for updates at the App Store it says no app updates available, why isn't it checking for an upgrade? All the boxes are checked in settings to allow mac os updates. Its currently running High Sierra 10.13.6.