I usually boot to TWRP from fastboot directly using the latest image as I don't have it permanently installed. Then I wipe system and cache, install the rom and reboot to bootloader. Then I boot into the same recovery again via fastboot, check that the slot has switched (A<>B) and flash the rom again. Then I boot to system and that's it.
In short, you'll want to reboot into your Pixel Experience recovery and use the ADB sideload feature in the same way you did to install Pixel Experience, only this time with the latest OTA zip you can grab from the official downloads (or with the 'export to internal storage' function of the updater + transferring the zip to your PC). Don't erase any of your data - you don't have to do so when updating between versions of a ROM.
fastboot boot <twrp-image-file>