Wired ESP device in integration, not in add-on

I have a wired ESP device that was discovered by DHCP and as a device in the HA ESPHome integration.
It’s working, the entities show up and report values.
Now I want to assign a fixed IP and make some minor modifications to the entities.
Am I right that this has can only be achieved through the ESPHome add-on?

As stated in the title: the device is not showing in the ESPHome add-on (which is up-to-date)
Restarted the add-on first and then HA but nothing.
I have searched here and on the ESPHome site but cannot find any info about this.

Is it possible to get the device into the add-on with the device only connected to LAN and not near the HA instance?

What device?

The add-on shows what YAML files it finds in the ESPHome folder.

Did you buy something like the Athom switch that has ESPHome pre-installed? If yes, then you have to obtain the ESPHome YAML file from the device maker.

Personally, I try to not use static IP addresses. I have over 100 WiFi clients and managing that many static IP addresses would be an unnecessary complication. I do use static IPs only on my servers. Otherwise, if the IP needs to remain the same because other entities rely on them, like cameras for example, I reserve the IP in my router.