[Lenovo Zuk Z2 Pro Questions & Answers] Terminator.J:
How did you get trojans on your phone?! And what makes you think that's what it was?

Okay, well, the bad news is you probably trashed all your data and will be setting up a new install as though you had done a factory reset. If /system was mounted as read-write, you probably don't get to go back to your old android just as it was unless you made a nandroid backup (that's the backup/restore option available through TWRP or CWM recoveries) and copied it to your computer before wiping. So, y'know, take a minute, take a deep breath, pour a drink, take a sip, and let that reality sink in. Sorry it happened.

I'm going to assume you're using some version of TWRP for recovery, because that's pretty much all there is for the Z2 Pro. Hopefully the 3.1.0 version from zukfans.eu, although if you got the 3.1.0 from LR.Team on the Chinese site, I'd like a download link. So just to make sure you've got nothing left, restart the phone and in the unlocked bootloader menu, go into recovery instead, go into the "Mount" button and make sure MTP is enabled, and plug into your computer with a good USB 3 type-C cable directly into a motherboard port (the factory cable can actually be kinda sketchy). If you go to This PC, see the "ZUK Z2121" MTP device, and can see "Internal memory" or "Internal storage" directory inside of that, then your MTP drivers are working correctly... and if internal memory is empty, then it's empty.

Gone.

Sorry. Take another sip and reflect on doing a backup (System, Data, Boot, and probably Persist in case you're planning on jumping between android 6 & 7) and copying that backup folder to your computer in-between each attempt to fiddle with things or start trying to sideload hacked PoGo apps from Russian sites.

Anyway, if that's truly the case and you've wiped out all the internal memory, you'll be reinstalling from scratch and you're not going to get all your stuff back.

You should probably plan to go to Advanced Wipe and clear out System, Data, Cache, Dalvik, and Boot. Don't touch Persist. Then make a new folder on the phone's internal memory (Installers or something), copy over a new ROM + Gapps, install it, reboot once into recovery just so TWRP can secure itself, then reboot into system and sign back in and start reloading all your contacts & apps & accounts & stuff.

If you have a backup, then copy it to your computer before anything else, take a backup of the current state, then restore the old backup.

In order for OTG (if that's what "ugt" is supposed to mean) to work, the adapter or thumb drive needs to actually support USB-OTG mode, and the memory card/drive needs to be 32GB or less, and formatted FAT32 (no exFAT, no 64+ gig thumb drives, boo). Go ahead and reformat it, then create a folder and copy the ROM+Gapps you want to install to it, plug it into the phone while in TWRP, go into the "mount" button and check the "USB-OTG" box, then go to Install, Select Storage, and choose "USB-OTG". Then you should be able to see the folder and install zips from the USB-OTG drive.

Good luck, and remember to take a backup and copy it to your computer for safe keeping when things are working, before you start trying to do weird things. Now finish that drink. ;)