There is a place to do that on your state income taxes at the end of the year. I'm not sure how no one at the state tax office would not know that, they have an easy to understand website. Alternatively, you can report it directly to them.

https://www.cdtfa.ca.gov/taxes-and-fees/use-tax.htm#Overview

Not all states have income tax

Sorry, it was an article about California, figured that was what we were talking about

fair enough, as a Washingtonian I sometimes forget that others have to deal with state income tax, definitely makes sense it'd just be part of yearly tax paperwork you already have to do.

From a quick google I think a lot of the additional confusion is the mix of Use/Sales tax when they mostly (as a customer) have the same meaning but for a tax authority have different meaning, searching for "Washington how to declare sales tax" turns up a bunch of random stuff about regulations for retailers showing sales tax correctly, if you search for "Washington how to declare use tax" actually brings up the correct documents from the state, I can def see some bureaucrat not connecting that that's what was actually meant.