Imagine the situation when your customer has placed the order using a different email and ask to reassign the order to the main account. It might by quiet challenging. By defaults Magento® won't allow you to assign orders that are placed as guest's ones to an existing customer's account or move orders between accounts. The Reassign Order extension for Magento® 2 helps to deal with this issue.
Now after your customer has placed the order using different email, you can reassign the order manually to another customer account from the order view. If your customer asks to reassign all orders to the main account it won't be a problem! You can just reassign multiple orders in bulk on the orders' list in backend. Besides manual settings the extension allows to assign new orders automatically on checkout after the customer used the email linked to the account.
Once the order has been reassigned, you can find the details in the order history section. Besides that, your customers will stay informed by email notification. You can also override the customer name or email on the order if necessary.