Dear Sapna,
Please have a look at the Documentation of the MATLAB function xlsread here. At this link you can find a method how to read the value of a certain cell. You could use an if statement to correct this cell if necessary. The change can stored in the excel file with the MATLAB function xlswrite. If the name of the file which you save is equal to the name you have read from, you can 'correct' your excel sheet with your if statement in MATLAB.
Good luck! Christiaan
