@Sequoia Meier , Apologies for the delay on this!
To better assist you on this, have hosted the WebApp on an Azure VM or Azure App Service or some other Azure service?
On Azure App Service, WebApp when created adds a default domain name. The URL of the web app becomes http://<app-name>.azurewebsites.net, where <app-name> is your app name.
If you have already acquired the domain name, to know how to add a custom domain name, see the detailed walk-through: how to map a custom domain name. This guide shows you how to map an existing custom Domain Name System (DNS) name to App Service.
The DNS record type ( root, subdomain, wildcard) you need to add with your domain provider depends on the domain you want to add to App Service.
Additionally, you may want to know.
Create a WordPress site on Azure App Service
Giving your existing WordPress MultiSite a new domain name on Microsoft Azure