I bought an Apple TV HD, it had a Siri Remote in the box. The next day I decided to go back and pay the extra for an Apple TV 4K. I exchanged it, paid $30 and got home to discover it contains a regular Apple TV remote, not Siri. What

The following may (or may not) help. See the information in Identify your Apple TV remote - Apple Support including the following:

*Apple TV 4K and Apple TV HD ship with the same remote everywhere. In countries and regions that support Siri, the remote is called Siri Remote. Elsewhere, it’s called Apple TV Remote. Siri works on either remote as long as your Apple TV 4K or Apple TV HD is set up with a language and country or region that supports Siri.

probably an old unit from before they changed the remote, return it

I still don't understand which remote you received -- but it doesn't matter because this is primarily a user-to-user support forum; other Apple users like you. You will need to return it if it is not the correct remote.

The Apple tv 4K second edition has a Siri Remote which looks more like the Older remotes known from appletv 2 and 3

if you wish you can continue using your appletv hd or appletv 4K 1 edition remote if you like