Q: Where is the option in Windows PC app for iTunes to back your installed apps from your IPhone6

Hello, p511dp. 

Thank you for visiting Apple Support Communities. 

I would need clarification on this question to possibly provide a better answer.  However, it sounds like you want to backup your purchased Apps and their data via iTunes.  The steps in the articles below will walk you through the process of transferring purchases from your iPhone and backup via iTunes. 

Re-download or transfer your iTunes Store purchases from an iPhone, iPad or iPod to a computer

Back up and restore your iPhone, iPad, or iPod touch using iCloud or iTunes

-Jason H.