EDIT: I misread. I don't know what an Amazon assistant is. I'm talking about an Amazon echo below
I have one at a cabin in the mountains that has no internet or cell service. It required internet access to sync/auth with my phone so I did it at home then moved it to the cabin. I think it needed to be auth'd to an Amazon account, despite never planning or wanting to use it with an account. It was a "prize" from work.
It is literally impossible for it to connect to the internet at its location but it is a pretty good speaker. Perhaps the loneliest IoT device ever, but I'd never use it in a connected state.
If you only want it for a speaker, you could wall it off to prevent Internet access even at home