You can add a custom domain using the deployment service that your site is using. See below for links to some common hosting providers. And see here for more information on Stackbit's deployment options.
If you do not have a GitHub account, or just need some additional guidance, we will be glad to help you. Please contact support with your project ID, which can be found in the URL when using the Studio.
For users who authenticated with GitHub and are using Netlify, you will need to log into Netlify and add your custom domain there using these instructions.
Netlify also supports registering new domains if you don't already have one.
Digital Ocean supports managing domains through its control panel and API. See here for more information.
At this time, Digital Ocean does not support registering new domains.
If you have deployed your site to Azure Static Web Apps, here are the instructions for adding a custom domain.
Azure also supports hosting your domain, but you must register new domains elsewhere.