Welcome to the Community. I'd be happy to assist you with deleting a posting that came from the Banking tab.
A transaction that was downloaded from your bank can be deleted with just a few clicks. Here's how:
I've included a brief video to serve as an example:
If the transaction has already been accepted into your register, here's how you can return it to For Review:
The following screenshot is a visual reference:
For additional information on this, such as how to restore excluded transactions, I recommend the following article: How to Exclude Expenses from Downloaded Bank Transactions.
That'll do it. I'm confident this information will have you on the path towards a resolution.
Please let me know if you have questions or need anything. Hoping this response finds you with a smile.