A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
It sounds like what you're looking to do is Find & Replace based on formatting attributes.
Excel for Mac does not have that capability. AFAIK the only spreadsheet software that does have it is the later versions of Excel for Windows... There may be another but I've never come across it.
I'm afraid that if the class is specifically on Microsoft Excel 2013 for Windows this is not the only assignment you won't be able to complete unless you're using that software.