To move your project to a different billing account, you must be a billing administrator and the project owner.
To see the current administrators, go to the Google Cloud Platform Console, open the left side menu and select Billing. If you have more than one billing account, select the billing account name. You'll either see the current list under Request access, if you aren't an administrator, or in the Permissions panel on the right side (if you don't see the Permissions panel, click SHOW INFO PANEL).
To confirm who owns the project, go to the Google Cloud Platform Console, open the console left side menu, and click IAM & Admin. Ensure that a project is selected to see the project owner.