Glad to have you here in the Community, @stewart4.
I'll share the options on how to reclassify your transfer to an expense.
If you used a cheque when transferring funds, you can go to the Expenses page. Then, open the Cheque and reclassify the category details. Please see the screenshot below for your reference.
If you transferred funds between two accounts using the Transfer feature, there's isn't an option to reclassify it to an expense. As an alternative, you can delete the transfer on the bank register (see the screenshot below). Then, create create an expense for the transaction.