A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
OK, so you're saying that your data is not in a table.
In this case, reapply won't work, because reapply required the data to be in a table, as documented. This is just how Excel works, whether you find that helpful or not.
So, the answer to your question "Reapply is grayed out, so what do I do?" is: Turn the data into an Excel Table. Then you will be able to reapply sort and filter.