Add and remove labels
When setting up the Labels field, select more (•••) > Add/remove values to add or remove specific labels to and from the existing set of labels. Using this option will override the default behavior of replacing all existing labels.
Add values to multi-select fields
By default, when setting up a multi-select field, you will set the values to the field, rather than add values to any existing values. In the below example, the result of the action will override any other values that were already exist on the Components field.
To add new values to the existing values on a field, select the Copy from issue options along with any new values to add.