Need my EF core to see already existing primary key in my SQL server table and work with it.

I have a SQL server DB table namely "RSBFileDetails", which has a primary key column "[File_Reference_Id]" auto generated int type. When I run my code to enter values in my DB using EF, I get an error: "System.InvalidOperationException: 'Unable to track an instance of type 'RsbfileDetail' because it does not have a primary key. Only entity types with primary keys may be tracked.'"

My code to enter data is: 

public async void PostValuesIntoDB()
        {
            DirectoryInfo info = new DirectoryInfo(path);          
            FileInfo[] fileInfos = info.GetFiles("*.trm");
            if (fileInfos != null || fileInfos.Length>0)
            {
                foreach (FileInfo fileInfo in fileInfos)
                {
                    RsbfileDetail detail = new RsbfileDetail();
                    detail.Filename = fileInfo.Name;
                    detail.FileUrl = fileInfo.FullName;
                    detail.FileType = fileInfo.Extension;                   
                    detail.CreatedDate = fileInfo.CreationTime;                   
                    await _rSBRepository.Add(detail);
                }
            }

 Highlighted code creates error message. 

public class RSBRepository : Repository<RsbfileDetail>, IRSBRepository
    {
        private readonly rsbsrdbContext _dbContext;        
        public RSBRepository(rsbsrdbContext dbContext) : base(dbContext)
        {
            _dbContext = dbContext;           
        }
        Task<RsbfileDetail> IRSBRepository.UploadFiles(string filename)
        {
            throw new NotImplementedException();
        }

        public async Task<string> Add(RsbfileDetail rsbfileDetail)
        {
            string dbresult = string.Empty;
            _dbContext.Add(rsbfileDetail);
            var response= await _dbContext.SaveChangesAsync();
            dbresult = response.ToString();

            return dbresult;
        }
        public void GetNewFileFromFolderToDB()
        {
            List<RsbfileDetail> result1 = new List<RsbfileDetail>();
            result1 = _dbContext.RsbfileDetails.Where(j => (j.Filename == "sample.txt")).ToList();       
            Console.WriteLine(result1);
        }        
    }

How can I get my code to insert values into my database. Please help me with this