Option 1: Search through every cell in a worksheet manually. (Don’t do that).
Option 2: use the Find and Replace function. To access this function:
a) simply press Control + F to bring up the Find and Replace menu.
b) Go to the Format drop down on the right hand side of the Find and Replace menu
c) In the resulting menu set the Font colour to white and click ok.
d) On the previous Find and Replace menu, select Find all.
e) If there is any white text in the sheet, the Find and Replace menu will show the cell coordinates at the bottom of the menu and the value hidden in white