The Canvas app must be downloaded
Go into your phone's settings and scroll down and find the Canvas app (The App name will be actually be "Student").
Click on the Canvas app and then click on notifications and allow notifications.
Now, open the Cavnas app and click the three lines in the top left, then tap "Settings".
Tap on "Push Notifications".
Here you are able to set what kinds of content you want notifications for such as announcements, assignments, etc.