Follow this guide:
https://vita.hacks.guide/updating-firmware-(3.74).html
In short, you can update to the latest FW 3.74, use HENlo in order to install VitaDeploy (which can downgrade your FW to version 3.65 or 3.60, whichever you like) and HENkaku, and then trigger the exploit for installing HENkaku Ensö (the permanent CFW).
I know there is some website that does this automatically from the Vita web browser, but I can't remember nor find it.