Hello @naas-nyankids,
At this time, there isn't an option to manually create the exchange gain or loss to post it in a preferred expense account. Because this is an adjustment automatically created by QuickBooks after collecting or paying a multi-currency transaction.
Here's an article you can read to learn more about this adjustment and how it works: Frequently Asked Questions about Home Currency Adjustments.
But I'd still recommend contacting your account for additional guidance in manually recording the exchange gain or loss. You can find one through this article: Find an accountant or bookkeeper.
Let me know in the comment section down below if you have any other questions. I'm always happy to lend a helping hand.