I just don’t know how you change affiliation at this point.

In California? You can do it online.

https://www.sos.ca.gov/elections/frequently-asked-questions

How do I change my political party?

In order to change your political party preference, you must re-register to vote. You can re-register to vote by completing a voter registration application online at RegisterToVote.ca.gov.

https://registertovote.ca.gov/