You have to FORMAT /data. wipe is not enough, because it is encrypted. Don’t forget to reboot in TWRP after format data. Otherwise you can’t push the file to your device
You can unpack the zx file (be sure you are using the right one (a-only or a/b)). Push the .img on your device and flash it via TWRP
If you are running into a bootloop flash vbmeta as here described [HOWTO] install eOS GSI on a Treble device - new GSI added June 14th