In the bottom left navigation bar, select [Menu] → Settings.
On the left side under General, select Account Users.
Hover on the user you want to edit and select [More] → Edit Access Rights.
Select [Toggle on] Give access to <Product> to give the user access to that product.
Use the drop-down menus to select the account user's role. If you select Custom, you can set permissions individually. Select View Details to see all the permissions that will be given with the chosen role.
View our article on Advertiser Account User Roles & Permissions for help with setting up roles & permissions.
Select Submit to save your changes.