To edit any of your tasks go to the project section and select the task in which you want to make changes. You can see three dots with every task name ( As shown in the image below ). Click on that option here you will see an option to edit the task.
Now, click on that edit option and make the required changes.
Note: Keep in mind that you have to click any of the sections of your screen after making the changes in the task. After following these steps your task will be successfully updated. You will see a notification at the top right corner when the task is updated.