This might help you You likely deleted the MDF file in Windows Explorer. SQL Server LocalDb doesn't know about it and the error is probably complaining about not being able to locate the MDF file. To delete it properly, you can delete the database from SQL Server Management Studio or SQL Server Object Explorer in Visual Studio.
will help you The (localdb)\ProjectsV12 and (localdb)\ProjectsV13 instances are created by SQL Server Data Tools (SSDT) and should not be used by applications (localdb)\MSSQLLocalDB is the SQL Server Express 2014/2016 LocalDB default instance name and an "automatic instance".
SQL LocalDB - Cannot delete a DB when its files are deleted
around this issue I use localdb in my wpf project app which use entity framework code first. When application running in first time local db database files are created to 'C:\Users\CurrentUserName' path as default. How to change this default path to another location which user selected. , Its as easy as this