1. Go to the first page of this thread and save "twrp-tb8703-3.2.1-20180825-bootsign.img" in your SD.
2. Boot in TWRP, press Install, Install Image, select saved .img, Recovery, and Swipe
3. Reboot in TWRP. Your TWRP will be updated 3.2.1. Try install LOS.