Security Error LG G4 (Bricked?) i think

i was freezing and uninstalling apps last night and must have removed something critical to the operating system. Now my phone will only load the Security Error screen with (authetication failure) in small print. i've been told that my phone isn't bricked but that i need to reflash the image. Im currently in Download mode but don't know what to do next. i have the rom image that i initially rooted the phone with. Thanks in Advance. peace