Create Guest User Sharing Rules Before Enabling Secure Record Access
Where: This change applies to all communities accessed through Lightning Experience and Salesforce Classic in Essentials, Enterprise, Performance, Unlimited, and Developer editions.
When: Before the Secure guest user record access setting is enabled, we recommend that you create guest user sharing rules that replace the sharing mechanisms that you previously used to grant access to guest users. The timelines for the rollout and enforcement of this setting are published in Guest User Security Policies and Timelines.
How: From Setup, in the Quick Find box, enter Sharing Settings, then select Sharing Settings. In the Sharing Rules related list for the object, click New and select the Guest user access, based on criteria rule type.