How to import excel sheet having merged cells.

Yes, it is possible but when you want to read an Excel file with merged cells then the way to do that is a little different. Using OLEDB we can read the Excel file that has a header at the first row and the rest of the data is vertically grown with no merged columns (in other words a single-celled single value). But if you try to read an Excel file that contains a merged cell using OLEDB then the result will be that it is in an unexpected format. You can do this either by use a third-party DLL or you can use one that Microsoft provides, Microsoft.office.Interop.Excel.dll. For Microsoft provides, Microsoft.office.Interop.Excel.dll you can follow link https://www.c-sharpcorner.com/UploadFile/17e8f6/reading-merged-cell-from-excel-using-microsoft-office-intero/

For third party DLL you can use EPPlus. it is available on nugget package https://www.nuget.org/packages/EPPlus.  You can follow the link on stack overflow https://stackoverflow.com/questions/17172829/epplus-how-to-traverse-through-every-content-block-cell-or-merged-range-of-a as