You can't. Per the docs:
If your account supports EC2-Classic, you cannot use these procedures to create a default VPC in a Region that supports EC2-Classic.
In non-EC2-Classic region, you have the option via the console to create a new default VPC. So you could, for example, create a default VPC in us-east-2
if you have deleted the one that AWS created for you (as far as I can tell, AWS did create default VPCs even in "classic" accounts).
But the bigger question: why do you want a default VPC? The only benefit that it provides you is pre-filling some fields when you manually create resources.