Thanks for the info!First you need to flash TWRP recovery into your Poco F3.
You can find the download link of the latest unofficial TWRP for Poco F3 in this thread.
This video tutorial shows how it is done (credits to Munchy).
Make sure to download the PEX update on your phone.
After all that, you just need to Power Off your phone, then hold Power Button and Volume Up (you can release Power Button when you feel the vibration) to go to TWRP Recovery mode. Tap Install and map out the update and make sure that Inject TWRP is checked.
I hope this helps!