edit – Specific column cannot be edited, every other one can

After exporting an excel table to a SharePoint List, I would like to edit one of my columns to change the type from Single line of text to Choice. However, one specific column does not have the “Edit” option under Column Settings while every other column does. I have “No” checked for content approval requirement. What could be different about the specific column in question and how can I go about getting the option to edit it?