How to change an accounting period to 13-month for one year, then to resume 12-month for subsequent years?

Hey there, @dalila-kahar.

For now, changing the accounting period to 13-month for one year is unavailable in QuickBooks Online (QBO).

However, you can run the Profit and Loss report in the program. Then, create a custom date to show a reporting period of 13 months. Here's how:

1. On the left pane, select Reports. 
2. Find and select Profit and Loss in the Find report by name field.
3. Set the date range to define the four-week period.
4. Click Run Report.  

The following article contains additional information about this, as well as the steps for saving your customized reports: How to customize reports.

Don't hesitate to tag my name in the comment section below if you have other concerns or questions. I'm always ready to help. Have a good day.