You will need to use Conditional formatting for this. For example if you want to highlight duplicate values in Column B , right-click on the Column B and select 'Conditional Formatting' , specify the range say 'B1: B15' under 'Apply to range'. Under the field 'Format cells if' select the option 'Custom formula is' and enter the following formula : =countif($B$1:$B$15,B1)>1

In the 'Formatting style ' option select a color to highlight the duplicate cells. You will now see the duplicate cells highlighted by this color.

Hello Harish you can use the following formula to find out duplicates cells in your sheet.

=IF(A2=A3, "Duplicate", "Not Duplicate")

for detail you can visit the below link

Find Duplicate Values in Google Sheet or Excel?

Thanks a lot Sir, this method/ Trick of Google Sheet save my time and effort.
Many thanks.