You can assign a Task to a teammate, as well as an assistant teammate to help. If you want to remove the assistant from the Task,

1. Select the task name to open up Task details.

2. On the right side, click Assist. You will see a checkmark beside who is assisting on the task.

task-assistant

3. Select the name to remove the checkmark.

task-uncheckassistant

4. Click Done.