How to flash a rom to a phone under bootloop
I've read the thread you linked and inspected the TWRP package inside. It looks like flashing for this device is incredibly simple, similar to a Nexus - it just flashes and boots a recovery image from fastboot. Lenovo even included a handy command to reboot straight to recovery from fastboot, which not even Nexus devices have.

Since you've flashed TWRP successfully in the past, I assume proper drivers have been installed, and you still have the whole folder on your PC. So right now what you're gonna do is boot your phone to fastboot, connect it to PC, open a command prompt window on PC then execute...

fastboot oem reboot-recovery


...which should take you to recovery.

If an error pops up then you might need to manually point to the fastboot location (drag the fastboot.exe in tools/ to the command prompt window), so it becomes something like...

C:\TWRP\tools\fastboot.exe oem reboot-recovery


(your path will vary).