You can create a concept model in an existing project from Project Explorer.
Procedure
In the Project Explorer, right-click the Business Objects folder and select New > Concept Model.
Name the concept model and click Finish.
Tip: Alternatively, if you select New > Business Object Model and click Next at the first dialog of the Create Business Object Model wizard, you can select the option to create a concept model. See Creating a Business Object Model in an Existing Project
.
In the Project Explorer you can confirm that the concept model has been created: