I did this in the ‘old’ (supported I know) HA Container by using the lovelace submenu in Configuration from front end.
I have moved to HA Supervisor and I can see the .js files in /usr/share/hassio/homeassistant/www (all good - and so are the other .yaml files in there) but I cant seem to find anyway in the front end to add resources. They used to be an option, but now all I see is as attached
:
Im sure it used to be across the top?
Here’s the config screen
