In Excel if I need to discover if a user had changed data or not , Where and what was original data written before this amendment?

first of all its depends if this excel is share  work book or unshare workbook.

please try my example below inorder to find later what excatly had been changed.

first of all open an excel  put any data table in it.

2) go to File--option-trust center-trust center setting-privacy options- clear the checkbox for  "Remove personal information from file properties on save"

3)go to review ==> click on share workbook==> put check box on  " allow changes by more than one user at the same time - ok

4)then try to change something from the table such as1000$ instead of3000$ etc then save and close the excel

5) open the excel go to review- track changes-accept reject changes- put check box on when :Not yet reviewed and put check box who: Everyone - ok

6) you will find the change and you will accept it ot reject and you will know form which pc the change had done.

hope i have giving you what you need