How do I insert customer order by customer Id?

Hi, I have a web application that different companies are using and these companies have their customers. My challenge is, these companies search and insert their records based on their company username which is working fine, but the issue is, for these companies to insert or search their customer orders with customer Id is really giving me nightmare. Please How do I do this?. I want each company to still use their company username because that's what I used to check is the user is authenticated, but when their are inserting their customers orders I want them to do that by inserting the record by their customers ID.