[GNC] How to Manually Match transactions

[Griff]

Here is a very simple question but I can't figure out how to do this.
I have searched the documentation and this mailing list.

How do I manually match 2 transactions:

I have 2 account that have had data imported via qfx.

Account 1 (credit card) has a transaction on 2020-01-19 that is a payment
for $amount which is the credit card payment from checking account

Account 2 (bank account) has a transaction on 2020-01-21 that is a
withdrawal for $amount which is the checking account payment to the credit
card.

The Transfer for the transactions in each account are currently  set to
Imbalance-USD. When I change the Account 1 transaction Transfer field to
Account 2 - a new transaction is created in Account 2 instead of matching
to the existing one.