First, the decedent's express instructions within a particular online platform or service provider shall take priority. That is, if a decedent provided a provide a "legacy contact" through account settings or preferences, such as in Facebook or Instagram, that named person shall inhereit the account.
Second, if the decedent did not make a designation within a service provider, or if the service provider does not provide for a designation option, the decedent's will shall govern. In this case, services such as Twitter or GoDaddy may require providing documentation, such as a death certification along with estate administrator papers along with photo identifications, in order to faciliate a transfer of ownership and access.
Third, if the decedent's will is silent on disposition, the service provider's term of service shall govern.
The full text of the bill can be found at https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=201520160AB691.