This guide assumes you already have a working and running Home Assistant server. If you don't, be sure to visit our Set up Home Assistant with a Raspberry Pi guide first.
Start out by logging in and opening up your Home Assistant dashboard and checking that the File editor is installed.
As part of the setup, you should have an add-on either called configurator or File editor with a wrench icon next to it. Go ahead and select it.
If you don't see it, it may not be installed. You can find it under Supervisor → Add-on Store → File editor and go through the installation procedure.