Change HomeKit hub on iPad to apple tv

You really can’t change which device is connected as the Hub. They switch around on their own and usually favour Apple TV’s and HomePods Apple TV has no home app and you can’t set things up on it.

You can disable the iPad as in the screenshot shown below, but please read what it says.

First in your ATV Settings make sure that it is enabled as a Home Hub. Then go to your iPad Settings, select the Home app settings and turn Home Hub off.

It seems that all Home Hub enabled devices share the task of hosting the Home Hub via a sort of local "cloud" of Homekit data and any one of them can take over hosting at any time.

Please review

Set up your HomePod, Apple TV, or iPad as a home hub - Apple Support