If your organisation has "Second level of financial approval" enabled in Payment Settings, then when viewing a project there is a "Payments reviewer" section. This will default to the organisation's financial controller or creator. By clicking on their name, a confirmation modal will prompt you to select one of the project’s managers as a Payments Reviewer.
This selected manager will then be able to approve worksheets and expenses for this particular project. Please note you will not be able to remove this selected Reviewer from the project. You can only remove this person from the project by first appointing another manager as Payments Reviewer.