First, you have to create a task by typing
/assign in the message box followed by the Task name and press Enter button.
After pressing on the enter button a dialog box will be displayed. Here you can add a due date and the assignees of the task or you can also assign the task from ‘Actions‘ tab after creating the task.
Your assignee can quit yourself from a specific task, Go to the channel and click on the ‘Actions‘ tab of the selected task and click on ‘Unassign‘ option from the dropdown list.
After selecting the ‘Unassign’ option, you will be successfully unassigned from the task.