The latest firmware update for Open Mobile LG Optimus F5(LG AS870) is “AS87011d”.
Here you can download the LG Official Stock ROM / Firmware revision “AS87011d” which can be used to unbrick or unroot your device.
You can use this stock rom to reflash your device or use the LG MOBILE SUPPORT TOOL software by LG Official to recover your Cell Phone.
or you can download LG_KDZ_FW-Update_OfflineFix.zip from xda forum here. The Tools can be used to flash .kdz format ROM.