I'm here to help you fix the error. First, I'd like to know what specific error you're referring so that I can provide the best resolution for it.
For now, I'd suggest to double check how you've mapped the details of the file. You can also download a sample file to help you with the column header and the specific information you're going to enter in the file. Then, follow the on-screen instructions.
I've added an article that you can check out to know more details about importing CSV file to QuickBooks Self-Employed:
I'm getting an error message when trying to import my CSV file
Thanks for your help. I think it's because there is an error in the formatting when downloading the file from Revolut. For some reason the columns are all merging once it's downloaded into Excel so think it's an issue with Revolut rather than Quickbooks