Go to https://twrp.me/Devices and download the correct version TWRP for your device.
Boot into boot loader menu
Plug you phone into a computer that has fastboot installed and run
sudo fastboot boot Downloads/twrp-3.3.0-0-sailfish.img
Note you may need to unlock your boot loader.
Your phone should now boot up into TWRP
![](https://www.incredigeek.com/home/wp-content/uploads/2020/03/Screenshot_1970-01-18-15-36-29-576x1024.png)
Swipe to Allow Modifications
![](https://www.incredigeek.com/home/wp-content/uploads/2020/03/Screenshot_1970-01-18-15-35-38-576x1024.png)
Select advanced
Then hit ADB Sideload.
Swipe to start the sideload and then sideload from your computer
adb sideload image.zip
More detailed explaination
https://www.cyanogenmods.org/adb-sideload-twrp/