You don't need to download/flash a ROM if you want to install TWRP on your device, so you can skip step 4, 9 and 10 (+ do NOT format data and do not use adb push command) from this guide.
Thank you, but I saw in several guides that it was necessary (not to reset) to install the version that was already on the phone. Are you sure the phone is not going to get stuck on twrp?