I'd tried the self employed app but now paying to use my accountants account but it won't show past mileage from the old app accumulated, can I download it somehow ?

I can assist with your mileage concern, Guy.

Currently, we're investigating the mileage issue in QuickBooks Self-Employed (QBSE). Please be assured that our engineers are working diligently to resolve this problem.

I recommend contacting our QuickBooks Support Team so that you'll be added to the list of affected users. This way, you'll receive email updates on the investigation's status and be notified once it is resolved. To expedite the transaction, provide investigation numbers INV-113106 and INV-114525.

To access QB Assistant from your browser, go to Assistant. If you’re using the QuickBooks Self-Employed app, tap the + button, then select Ask QB Assistant.

The details on how to get in touch with the support are outlined in this article: How to contact QuickBooks Self-Employed Support.

If there's anything else that you need help with QuickBooks, please check out this page: QuickBooks Self-Employed Overview.

I've got your back if you need more help. I'm always happy to lend a hand.