Numbered column appeared before the workbook. No idea how to fix this!

One of the auditors I work with pushed something, I don't know what, and this odd grey column is now on the left side of the report. I have been looking for something that looks out of the ordinary to make it go away but haven't found anything. I would greatly appreciate any help and have attached a screenshot. This one has me stumped and I don't know what to call it to Google the problem.

Thanks!