Hello, Gavin.

It's strange that when you tap the menu bar on your QuickBooks mobile app, the Help & Feedback option isn't there.

This unexpected behavior could have been brought on by out-of-date data that was kept on your QuickBooks mobile app. Before uninstalling the app, let's clear some app's data directly on your phone settings.

Here's how:

1. From your phone's settings, select Settings.
2. Click on General, then choose iPhone storage.
3. Look for an app that takes up a lot of space.
4. Tap Offload App to free up the storage without deleting the documents and data for the app.

After that, check if the option is already available. If not, proceed to uninstall and reinstall the app. 

You may also consider sending invoices using your mobile web browser as an alternative. Refer to this article for more detailed information: Create invoices in QuickBooks Online.

Do you want to improve your company's brand by adding a well-designed logo? If so, I've included this resource which provides the guidance needed to accomplish it: Add, customise, or remove logos on sales forms.

Feel free to post again if you need anything else. We're always here to help you.