SIR'd to Cal Poly, need to withdraw

I hope someone can help me with this. I SIR’d to Cal Poly as an incoming freshman and I was excited to go, but I got into another school from the waitlist, so I need to withdraw. I’ve been searching on the website and on my cal poly portal, but I can’t find anything about withdrawing, or canceling my SIR. Thanks

Call admissions.

I just emailed admissions, and if I don’t receive an email back on Monday I’ll call them. Thanks