In order for the FR Privacy App to properly load into your router settings, the router must have an Internet connection as the router powers up. If the router powers up without an Internet connection then the App will not properly install.
DO NOT WORRY AND DO NOT RESET YOUR ROUTER.
In the case you have been redirected to the FlashRouters Help Center, this means the Privacy App was installed correctly, but that the router simply did not have an internet connection when it was plugged in.
If you now have an internet connection through your FlashRouter (likely the case since you are able to access the Help Center), reloading the FR Privacy App is very simple, just REBOOT your router.
As long as your router still has an internet connection when you reboot, once the router finishes powering back up you should be able to access the FR Privacy as usual by either navigating to www.flashroutersapp.com or by clicking on the Status > MyPage tab in your DD-WRT GUI settings.