Oops - I guess that needs to be better signposted...
If you go to the currency page in the dialog (where you're creating USD), there's a "Default Currency" dropdown in the main section on the right. You might need to close out of any currency you're editing, but hopefully it's reasonably prominent once you do.
If you go to the currency page in the dialog (where you're creating USD), there's a "Default Currency" dropdown in the main section on the right. You might need to close out of any currency you're editing, but hopefully it's reasonably prominent once you do.