Cant Root 5.0.2 on Lg Gpad 7.0

Hi im new to xda and dont know if im posting this in the right section but my problem is that my tablet wont root and i've tried everything is it possible to downgrade? or is there something im missing? i usually use kingroot but it saids theres no solutions please someone help :(

gpad 8.3 only boots into twrp, can't go into download mode

I had version v50020d, flashed twrp from the play store app I think. It's rooted. I did a factory reset and it got into twrp and never booted the system. I followed some tutorials for ota softbrick for g2 and some others and now it mounts data but everytime i reboot it, it seems to not mount system by default, so it boots into twrp. I wiped the system as some site told me and i think i messed it up. I flashed cm12 the september stable version. I seriously need your help. My gpads battery level is pretty low too. I really need to get it working again.