Occasionally you find that your spreadsheet has changed such that instead of having the columns as letters (A, B, C etc) they now appear as numbers (1,2,3 etc). You will also see that formula now use a R1C1 reference style. So how do you change the Excel columns back to letters (or in the same way, how to change the Excel columns to be numbers and use R1C1 formatting).
If this has happened to you accidentally i.e. you didn’t purposefully switch on R1C1 referencing , don’t worry as your spreadsheet is exactly the same, it is just a different way that Excel shows the rows and columns. You can easily switch it back and it will work fine.
The solution is in the options part of Excel. If you go to Excel Options (see below)
Then go to Formulas and switch off (or on) the R1Ci reference style.