This is May from Shopify.
Welcome to our Shopify Forums! That is a good question. I can understand how forgetting to update your POS location can cause some troubles. At this moment, unfortunately editing past orders/transactions is not something you can do on Shopify yet. There have been many merchants who requested for this feature as well, and I will add your vote the the existing ballot our developers review. In the mean time, although not ideal, you can add a note to these orders indicating that the order was made from a different location.
I do hope we can see this feature implemented in the near future. If our developers release this feature, they will announce it on our Announcements page. Thank you very much for bringing this to our attention.