Hi stephane5,
Using the project feature is a great way to ensure that you can track your job's profitability in your account. QuickBooks Online is a powerful program that offers the project feature to track your jobs costs and keep everything organized in one place. I'll be glad to provide you with some information on the possibility of changing the attached customer in a project.
In QuickBooks Online, if you've assigned a customer to your project, you cannot change the attached customer in a project. You'll have to delete the project and create a new one with the correct customer information.
To delete the current project, click the Projects tab from the left navigation menu > click the drop-down arrow next to Options in the Action column on the right-hand side > Click Delete. You'll need to note all your important information or all the transactions for that project before you delete it. Once noted, you can refer to them to create the new project with the correct customer.
The other option is to change the customer name to the new one by editing it under the Sales tab.
If the ability to change a customer attached to a project is something you'd like to see available in QuickBooks Online, I'd recommend providing sent us Feedback under the Gear icon in the top right corner of the dashboard. This is sent to our development team to be considered for future updates.
Let me know if you have any questions, I'll be happy to help.
