@inejghafa Have you tried logging-in at https://my.usc.edu/ ? It should guide you in getting setting-up. Or, it should be able to tell you if the email you used when applying is already linked to an active USC ID.
If none of that works, you can always look up your assigned admission counselor and ask them via email…
https://admission.usc.edu/findyourcounselor.html
Good Luck