I cannot find the settings app icon on my Apple Watch Ultra

Have to agree with you. The watches app layout is not normal at all for a real Apple Watch. I would recommend the buyer return the watch for refund, if they can. It's not an Apple Watch.

I hate to break it to you but your Apple Watch is fake.

Where did you buy this Watch? This is what a normal Apple Watch apps layout would look like for the Ultra:

Also, you cannot delete the settings app on the Apple Watch. The fact that yours came without it is even more strange.

Unfortunately, sometimes Apple serial numbers may be active, but not match the product you have. Your serial number is probably matching to a different watch somewhere around the world, specifically stolen or locked ones. Sorry to say but I think you have been scammed.

You should even read our very own lobsterghost1’s user tip on the risks of buying Apple products from others, its an excellent article!

The All Too Common SAD Reality of Buying … - Apple Community