Quickbooks online is auto assigning every Paypal sale to my oldest open invoice in QB. I can't change or View the paypal transaction to change it from "For Review"

This happens if QBO detects only one match to the transaction coming from PayPal, ratzco.

Since you can't change the PayPal transaction in the For Review tab, I'd suggest excluding it. Then, proceed with recording the payment manually.

To exclude a downloaded transaction:

1. From the left menu, select Banking.

2. On the Banking page, select the For Review tab.

3. Select the checkboxes of the transactions to exclude.
4. From the Batch actions drop-down, choose Exclude Selected.

I'll be here if you have any follow-up questions.