1. Login to Workast using Slack credentials
2. On the top left hand corner, click on your name 
3. Click on 'Preferences'
4. Here you can customize which notifications are sent to you through workast (under Apps) on Slack
5. At the bottom of the page, under the Notification heading, you will find sliders to turn off notifications for when you are assigned to a task.
6. This setting is turned on by default, slide it to the left to turn it off.  A pop-up will appear, confirming that your preferences have been changed.