Welcome to the Community. I'd be glad to lend a hand with changing the invoice label to pledge.
The label of your invoices will depend on the option selected from the Account and Settings of your QuickBooks.
Check out this sample screenshot:
If you also want to check the customer label, you can follow these steps:
I suggest bookmarking the article for your reference into configuring company settings:
How to configure company settings.
Please let me know if there's anything else I can do for you with regards to the invoices. I'll be here to help.