Allow Visitors to Join Your Community by Email or Phone
Where: This feature is available in all communities, accessed through Lightning Experience, Salesforce Classic, and all versions of the mobile app. Communities are available in Enterprise, Performance, Unlimited, and Developer editions.
How: Enable configurable self-registration on the Login & Registration page of the Administration Workspace. Choose the Configurable Self-Reg Page registration type, which generates a self-registration handler that you extend in Apex. You can locate the handler from the Setup Apex Classes page. Its name begins with AutocreatedConfigSelfReg.