Changing values in a column, when column label contains a number

Hi @Toz, welcome to RStudio Community.

It's hard for us to help you without seeing your data. It would be great if you could create a reprex (reproducible example). Read the following link for more details:

However, from the error message, it seems that you've referenced a variable that does not exist in your data frame. Are you sure that your variable is called Turnover GBP 2019 and not Turnover GBP?