Normal attributes can be set using setAttribute('attribute_handle', attribute_value). However trying to set an attribute using a multi - select express attribute does not work as desired in this way. For example I have a user attribute which is an express multi select which holds a list of facilities a user is assigned to manage. I want to import a csv containing new users and assign their facilities based on an array in one field of the csv. But using setAttribute() won't allow this with the express multi select addon.