How can I move all tabs on Safari on iPhone to a pre-existing tab group?

I feel like I've done this before successfully , or maybe that's a false memory and I never did. I've certainly can do it on iPad, but this is why I think Safari can be very unintuitive. I looked through the UI of iPhone Safari a few times and couldn't figure out how. I can put all tabs into a new tab group, but not append them to one that was already created.