WordPress multisite subsites may be mapped to an non-network top-level domain. This means a site created as subsite1.networkdomain.com, can be mapped to show as domain.com. This also works for subdirectory sites, so networkdomain.com/subsite1 can also appear at domain.com. Before setting up domain mapping, make sure your network has been correctly set up, and subsites can be created without issues.
Before WordPress 4.5, domain mapping requires a domain mapping plugin like WordPress MU Domain Mapping.
In WordPress 4.5+, domain mapping is a native feature.
Make sure the domain you want to use are already mapped to your server. If you have a dedicated IP address, you can point the A records for mappeddomain.com to your server. If you do not, you'll need to configure the nameservers for the mapped domain properly.
In the network admin dashboard, click on Sites to show the listing of all the subsites, and then click on edit for the subsite you want to map to. In our example, this is subsite1.mynetwork.com.
In the Site Address (URL) field, enter the full URL to the domain name you’re mapping -
http://mappeddomain.com - and click save.