Can I change the due date to the 1st of the month in the app

I'm delighted to have you here today, Richard.

To edit the due date inside your invoice using QuickBooks Online Mobile, you'll want to access the invoice and then click the Pencil icon at the top. I'll write down the steps and provide visual reference to ensure you're able to get through this.

1. Access your QuickBooks Online mobile.
2. Locate the invoice and then click the Pencil icon at the top of your invoice.
3. Go to the Due on section, and then change the date.
4. Once done, click Save.

See the attached screenshot for reference.

Moreover, I've got this article in case you'd like to modify an invoice payment inside the mobile app: Edit an invoice payment using the QuickBooks Online app.

It's been a pleasure to have you here in the Community space, Richard. Let me know if you need help accomplishing goals inside QuickBooks. I'll be here, ready to assist you. Stay safe, and have a great week!