1) In Visual Studio, go to Server Explorer and check if the ".mdf" data Connections for this project are connected, if so, right click and delete.
2 )In Solution Explorer, click Show All Files icon.
3) Select App_Data, right click and delete all ".mdf" files for this project.
4) Delete Migrations folder
5) Open SQL Server Management Studio, make sure the database for this project is not there, otherwise delete it.
6) now go to the Package Manager Console in Visual Studio and type:
7) Run your application
Note: if you get an error, in step 6 part 3 "Cannot attach the file...", it is possibly because you didn't delete the database files completely in SQL Server.