Hi Suganya,
Thank you for using Syncfusion products.
We can acheive the above reported query using the below code with XlsIO.
Code Snippet[C#]:
IWorksheet worksheet = workbook.Worksheets[0];
//TODO:Please provide the code for unlock cells
worksheet.Protect("syncfusion", ExcelSheetProtection.UnLockedCells);
Please try the above code and let us know if this helps you.
Please go through the following online document for more details.
http://help.syncfusion.com/ug/asp.net/xlsio/default.htm#!Documents/howtoprotectcertaincellsinaspreadsheet.htm
http://help.syncfusion.com/ug/asp.net/xlsio/default.htm#!Documents/worksheetprotection.htm
Please let me know if you require any further clarifications.
Thanks,
Sridhar.S