The default SOA administrator in a SOA/BPM installation is "weblogic". The SOA administrator, amongst other tasks, is the BPM Workspace administrator, the out-of-the-box web-based interface where users can access and manage their tasks. This is just fine for development and testing purposes.
However, at some point during your process lifecycle you will be faced with the task of creating and assigning a custom SOA administrator other than "weblogic" to serve your processes' administrative tasks, for example, mapping application roles to users and/or enterprise groups.
The first thing that you need to do is of course create your new SOA admin user using the Weblogic Administrator Console.
There are a couple of ways to do so.
The first and most easiest way is by assigning the "Administrators" group to your new user as in the image below.
A much better approach would be to map your new user to the SOAAmin application role using the Enterprise Manager. To do so, right click the soa-infra node and from the context menu select "Security > Application Roles"
On the "Application Roles" page enter SOAAdmin in the search box field and click on the search button. You should see the SOAAdmin application role displayed in the search results page and selected.