Assigning the right Approvers and Controllers to the right projects can be done in two different ways:
1. By appointing an approver to a project
You go to 'Settings' - 'Company Settings' - 'Projects' and select the project you want to assign your Approvers/Controllers to and in the right fields you can click and select the users you want to assign.
2. By giving approval permissions to a user
You go to 'Settings' - 'Company Settings' - 'Users' and select the user you want to assign as your Approver/Controller of a specific project. Under the 'Roles' you can check the Approver and/or Controller box and click in the project field and select the right project.
In case of an approval conflict because the Approver/Controller can also be a member of the same project. You can add an alternative Approver/Controller under 'Settings' - 'Company Settings' - 'Projects'.