Can you clarify what expenses you're referring to that you'd like to update? I want to make sure that I'll be able to provide the correct instructions that you're looking for.
If you submitted bills or expenses to your vendors outside QuickBooks, you can resend the updated ones. Simply find and edit them from your Expense Transactions list. Then, print and send them using your channels outside QuickBooks Online.
Here's how:
Click on the Expenses menu.
Under the Expenses tab, you can find all your expenses.
Adjust the filters to find the type of data you want. Click Apply.