A change of your business's details in ⚙️Settings won't alter your documents retrospectively - such action would create quite a mess in your previous documents. If your business details changed, change it first under Settings - Business details.
Then, if you need to change your business details on a specific invoice
on the Billdu website edit the invoice, select Edit business details. A window appears where you can edit all your company details for that specific document
If you've added a logo or signature to your Business settings, it will show up on the first invoice you create AFTER such change. In case you need a logo to show up on your invoice, upload a logo to your business settings first and create a new invoice (you can also use the duplication feature)
HINT: It's possible to change your business details for your very first 3 invoices in the app click on your company name, your business details appear and you can change it for all documents