how does source value automatically stores in different source medium

Summary:

Content (please ensure you mask any confidential information):

Hello,

I understand under 'Candidate Dimensions Source Names' we can add new source names , but how does these source names gets mapped under Source medium.

For eg: we have LinkedIn, facebook etc. but how is that under social media it populates only LinkedIn, facebook and twitter ?

where is this configured ? how can we add more under social media or how can we add more source under any other source mediums ?

Version (include the version you are using, if applicable):

23c

Code Snippet (add any code snippets that support your topic, if applicable):