Update customer metafield after checkout a order

[nhtbao101]

This is the first time I am working with Shopify, please help me with this case.
I am using points in the customer metafield to discount for an order when the customer checkout. But I don't know how to update customer metafield on checkout page
I want to know how can I update the customer metafield after I checkout an order or submited an order successfully?
If possible, how can we do that? Thank you so much