How do I add a logo to invoices on the quickbooks online app

Hello and welcome to the Community 

To upload your logo on the QuickBooks Online mobile app, select Menu > tap the Gear icon > Company information. Here, you choose Upload your logo to browse from your device's library. 

For further information on customising invoices in QuickBooks Online, check out our Community guide. Thanks for reaching Intuit support. We'll be here if you need any further assistance.