I want to update the order email id from the admin when you see the order detail, note I don't want to update the customer email id, Just want to update the email address for order only.
Here is step by step guide to achieve the above -:
Step 1 : Go to your phpMyAdmin or sqlyog for your Magento 2 store database
Step 2 : Run the following query against your Magento 2 store database
update sales_flat_order set email@example.com' where firstname.lastname@example.org' and increment_id='100000003'
Please take back up before running any delete / update / insert statements against your live database
The above will work for limited amount of requests you get to update or modify email address from your customers.
But if you get a lot of requests or you are not familiar with phpMyAdmin or sqlyog then we would highly recommend you to use the following module as this module allows you to edit email address via admin interface.