Basically you can't. You have to unconfigure and reconfigure it on new databases, so usually it is easier just to rebuild from scratch.
Migrating BizTalk Servers from one domain to another domain isn't supported The Microsoft BizTalk Server installation and the BizTalk Server databases in Microsoft SQL Server contain domain-specific information. In this scenario, the following actions aren't supported: Moving an existing BizTalk Server installation from one domain to another domain. Moving the databases associated with an existing BizTalk Server installation from one domain to another domain.
Workaround
If you want to move an existing server, you must use the ConfigFramework /u
command to completely unconfigure the server before you migrate it to the new domain.
This command removes the current configuration and the existing BizTalk Server databases. Once the server is in the new domain, you must run the Configuration Wizard to reconfigure the server to create a new group that has a new set of databases.