How can I set up an Apple Watch with a different cellular carrier than my iPhone?

I got an Apple Watch for my kid that has cellular service, but my current mobile carrier (on a business account) won’t let me add my kid’s Apple Watch to the plan. I ended up signing up for a different carrier just for the watch. But when I try to add cellular data to the watch, it keeps trying to pair with my current mobile carrier.

How do I switch the Apple Watch to a different carrier than the one on my iPhone? I used to do this in the past, but with this new watch, it’s not an option anymore.

Can anyone help me figure this out?

I don’t think you can do that since the watch is tied to the phone.