I'm happy to help you set up the statement in QuickBooks Online.
If you're referring to a customer statement, you can just go to the Customer's profile to set up this one. Let me guide you on how:
Go to the Sales menu on the left side and select Customers.
Check the checkboxes for the customers you want to make statements for and pick Create Statements in the Batch actions drop-down.
Choose a statement type and date range in the field.
Hit Save and close.
In addition, if you want to change the statement text form, go to Account and Settings and make the necessary changes. For your convenience, here are some sample screenshots: