Define a My Domain When Creating a New Salesforce Org
Where: This change applies to Lightning Experience and Salesforce Classic in Group, Essentials, Professional, Enterprise, Performance, Unlimited, and Developer editions.
How: Specify your new org’s My Domain name during sign-up using the My Domain field. If the requested My Domain name isn’t unique, the sign-up process adds characters at the end of the name. For example, if you request “example” as your My Domain name and it’s in use, the sign-up process can adjust it to “example1” or “example-1a”.
If you don’t choose a My Domain during sign-up, Salesforce assigns one for you based on your company name. If you don’t like the one we set, you can change it.
If you maintain a sign-up form for Salesforce orgs, we recommend that you add the My Domain name field.
To change your My Domain name, in Setup, in the Quick Find box, enter My Domain, and then select My Domain. Under My Domain Settings, select Edit, and then enter a new My Domain name in the Rename your My Domain field. Select Check for availability, and if the domain is available, click Save to submit your new My Domain for provisioning. After provisioning is complete, deploy your new domain for your changes to take effect.