The SCCA licensing process is of Byzantine complexity. Appendix C of the GCR gives all the details. The tldr is:
1. Join SCCA. You must be a member in order to enter a race, even if you race on your SVRA license.
2. You can enter Regionals with your SVRA or PCA license. You must still be a member of SCCA.
3. If you want an SCCA Full Competition license, contact your Divisional License Administrator. In my experience, they are very helpful.
From your profile, I am guessing that you are in Central Division. Licensing contact here:
https://cendiv-scca.org/about/contacts/
Click Road Racing Officials, scroll down to Driver Licensing.
Other divisions show/hide that information in various places, including the divisional web page. If you cannot find your person, contact your Divisional Executive Steward.
Exec Steward contact info here (in the SCCA member portal):
https://my.scca.com/eweb/dynamicpage...tteecode=EXSTW