One employee I pay just once per month. In error, his payperiod is set to run from the 2nd of the month until the 1st of the following month. How to fix to 1st - 31st?

Nice to have you here in the Community, @don47.

I'm here to ensure you can update an employee's pay period in QuickBooks Online (QBO).

You can simply follow these steps to proceed with modifying the pay period of an employee:

1. Go to the Payroll menu and proceed to the Employees tab.
2. Select your employee.
3. From Employment details, choose either Start or Edit.
   
4. From the Pay schedule ▼ dropdown, click the pencil icon to edit the pay schedule. Or Click + Add pay schedule to create a new pay schedule.
   
5. Choose a Pay frequency and fill out the appropriate fields, then pick Save. Toggle the Custom schedule button to see more schedule customization options.
   
6. Once done, select Save.

Here's an article for more details about this process: Set up and manage payroll schedules.

Additionally, check out this article to give you a closer look at your employee's total wages, deductions, and tax information for a certain period: Run payroll reports.

I'll get right back to this thread if you need more help managing your employees' pay periods in QuickBooks. I'd be glad to help. Have a good one!