I'd like to make sure that your reports are accurate, krish12.
Any changes on a reconciled transaction for 2018 will affect your financial reports. You may have to undo the entire reconciliation for that account.
I'd recommend consulting your accountant before following KhimG's steps.
I'm also adding this article for more details on how to unreconcile a transaction or undo a reconciliation.
Feel free to reach out to us if you need anything else. Thanks.