If you have a review after the first so many weeks or months, that would be a good time to bring up the need for new instruments. When asking for instruments, you want to explain why new instruments are important. In this article I explain why using worn out instruments aren’t a good idea:
https://www.todaysrdh.com/6-things-hygienists-wished-their-doctor-boss-knew/
If you don’t have any sort of review or regular team meetings with the doctor/office manager, I’d ask for a meeting to talk about your concerns. If you don’t ask, the answer will always be no.
On a side note, at the interview or working interview would have been a great time to inquire about how often instruments are replaced. Tip for next time!