How to flash Voice PE with custom yaml?

Hi all,
I’m following a thread about exposing the currently running timer from Voice PE, and someone posted a solution that involves flashing the device with a modification to the YAML. I’ve got the Voice PE configured inside Home Assistant at the moment, using the standard onboarding process for the PE. I have ESPHome installed and I understand how to use it in general; but flashing the PE seems to require the device to be adopted by ESPHome, and none of my Voice PE devices show up for adoption. All I see is the configs for devices which I configured completely through ESPHome.
Are there any steps I might be missing to get the device adoptable? Or am I doing totally the wrong thing?
Any help much appreciated.

Look for a black bar at the top of the ESPHome builder. That is where the device should be found. Click the show link and it will appear in the list to be adopted.

Found it, thank you!
My problem was that I have a Unifi network with the IoT things on a separate /24 subnet, and I had selected ping rather than mDNS as the discovery mechanism. Clearly ping only checks inside the same subnet (/24) and to discover items on the other subnet it would have to look at /16. Since mDNS forwarding is enabled on this network, that works across networks.